replacing stairs: risers and treads

Our current stage in our renovation project involves fixing up the stairs.

We removed the carpet and there are several cracked treads.

We pretty much have decided to replace the treads with new ones.

On a recent visit to HD I noticed that I could buy not only the treads but I could buy risers.

Why would I want precut “risers” when i could buy the 1 x 8 pine planks at a fraction of the cost and make my own.

Are the prefab risers “special” in any way?

Did they look special? I seem to remember that tread + riser = 15" - maybe their treads + risers added up to some dimension they thought right?

Just a word about wood at Home Depot: Look at the lumber mill’s tag on the dimensional lumber 2x4, etc. - most of the stacks are clearly labeled “Green”.
My father was not a particularly nice person, but he did know how to use tools (farm boy).
Rule one of lumber: NEVER buy green lumber.
Why? "Green means un-dried - sap still present. As is dries, it will warp, twist, split, etc.
IT IS WORTHKESS
You may wish to consider the wisdom of trusting any yard which sells such absolute crap.
You are about to spend a great deal of time re-working those stairs. If the wood fails 10 years down the road, you will probably wish you had found a lumber yard with more integrity than to sell crap to folks who don’t know better than to use it.
p.s. - if oyu look, you will find that H.D. does sell 2x4, 2x3, and maybe 2x2 labeled “K.D.” - kild dried. You want kiln dried lumber- you choose the source.
p.p.s. - Lowes matches H.D. with green and kd dimensional lumber.