For something like seeing sports equipment unused for a long time in someone’s house you don’t know if the stuff was bought and never used (the OP’s question) or if the owner played the sport regularly and then gave it up–and never decluttered.
Tools: I barely ever break out my sockets and even more rare to use my air powered tools.
Lots of guys at one time were into fixing cars but you get to a point in your life where you dont have the time to tear into an engine and create the mess and you just give it up. I havent changed my own oil in maybe 10 years so my oil wrenches go unused.
Another, sort of the same - pets.
The big lizard your kid thought was cool when he was 10 which can live 50 years, long past when they ever still want it.
Exotic and expensive birds which can live 30 years.
The horses you used to ride or you bought for your daughter when she was 14 but now is in college and now just sit in a pasture or you pay boarding fees for.
On the other hand what is the reaction when you suggest this pet should be given to a good home?
My personal one was a mulching leaf blower. I thought, well, it’s electric so that’s okay and even though I NEVER use a leaf blower to just blow shit around (that’s what rakes are for, hello!) I thought that one that would suck up leaves and chop them into easily composted bits in a handy bag was pretty snazzy. Until the first time I used it and found the one pile of dog shit I hadn’t seen the hard way. I mean, it literally HIT THE FAN. Yup, that was that, sits on a shelf in a shed to this day.
lots of games in my steam library have never been played for more than a few minutes.
I’m guessing - relief!
This question sounds like something you’d hear on the “Family Feud” show.
I would think those backyard jungle gyms. I often get the sense that more time was spent by the parents setting it up than the kids spent playing on it.
Lots of games in my steam library were so cheap that if I ever did play them for a few minutes I’d have gotten my money’s worth.
I’ve generally observed that those things get used to death.
Expensive-ish things I’ve bought and used far less than I should have:
- Treadmill (now sold)
- Exercise bike (going to be sold–it’s currently a coat rack)
- One of those fancy Kitchen Aid stand mixers (it’s a gorgeous turquoise color. I’ve used it once. I even got the pasta attachments for it, which have not been used at all)
- Blender (used twice to make booze milkshakes)
- Keurig (used several times, but not for a long time and now it needs to be cleaned out before it can be used again)
- Board games - SOOO many board games! I really want to play them, but scheduling for more than 2 people and learning rules makes that a daunting task.
- Guitar (still want to learn to play the damn thing)
- Bass (ditto)
- RPG books (I collect them, but I’ve probably read/used maybe 20% of them)
- Table for gaming (it’s a little too big for the room it’s in, which makes it inconvenient to use for actual gaming)
- Several motorcycles - they were used, but not nearly often enough to justify the expense. I finally gave up and admitted I liked the idea of motorcycling more than the actual act.
Yeah, I’m a sad specimen of stupid spending. I’ve gotten better over the past few years, though!
Used to have neighbors with kids. They had a trampoline in the backyard. Those kids were on that thing every day!
One year for Christmas, they got those kooky razor scooter things. They took them out, and bounced around with them on the trampoline! 
I’m pretty sure that backyard jungle gyms and trampolines follow the same pattern as swimming pools.
Our pool was amazing back when our kids were tweens–the pool was full of kids all day long every day in the summer months, and I would be working in my office listening to shouts of “Marco” and “Polo” amid splashes.
Now, fifteen years later, it’s just another thing to maintain…and soon to be filled in.
I bought a blendtec blender and haven’t taken it out of the box.
Same with an Instant Pot… seemed like something I’d really enjoy messing around with but just… haven’t?
Oh no. Backyard gyms are great. Really gave the kids something to do. We had a big wooden Rainbow system. Climbing on it. Jumping off it. Made a fort of it. Water balloon fights, etc… It cost me $900 for used and I sold it for $200 after about 12 years. They are monster heavy to move though.
And the trampoline, even better. Around $250 and we again got about 12 years out of it. We’ve had a dozen kids on that thing with the water sprinkler on underneath. The kids even put their tent on it and camped on it.
But yes, eventually they got too big for them and they were hard to mow around so we sold the gym and threw away the tramp because it was rusted out and unsafe.
Curious, how much to fill in?
Some friends years ago faced the issue of fixing a crack in theirs or just filling it in. I think they were quoted somewhere around $5,000 to fill in which wasnt much less than the cost of repair so they just had it fixed.
I have heard realtors say, unless the house is very big and expensive, most pools are more of a liability when you go to sell them.
We shall see…
My contractor is also a close friend, so I expect the price to be reasonable. He indicated that it would be roughly a few thousand, due to the cost of fill and the labor to make it look pretty.
One factor I didn’t think of: he wants me to find out from the township if they allow burying of the broken concrete debris in place or if we will need to have it carted away–an unknown that will affect the cost.
I’m puzzled about something. Are you talking about an in-ground pool? How would you sell that to a neighbor if it is?
I have a Suzuki Q Chord.
At least I didn’t pay real good money for it. I got it at the Goodwill auction. It will be handy for the drum functions if I ever get around to doing any recording. 
Cheaper in-ground pools are actually a framework of wood or other materials that is then covered by a liner—it’s kind of like if you built an above ground pool in a deep hole and backfilled around the sides.
Mine is like this. It’s not as flimsy as it sounds since this pool is probably 35 years old. You just need to get it re-lined every decade.
With that said, it seems a bit of a challenge to move such a structure to another resting place.