So why were all the buildings built at the top of impossibly tall stilts? Why didn’t folks live and work on the planet’s surface?
Because being on top of impossibly high stilts is cool.
Square.
Because the dinosaurs would have crushed the houses. Also, Fred Flintstone would have met George much too soon.
SSG Schwartz
I just assumed it was a smog thing.
Greenland and Antarctic Ice shelves. They knew, they knew!
I think that was actually kind of explicit, not so much the smog, but so they could rise above the inclement weather and live a Sunny existence all their lives. Smog is a decent interpretation as well.
To my knowledge, we never saw the ground in that show – everything was impossibly high up. There were even floating burger joints (presumably serving flying cow burgers).
There is one episode where they go to a Dude Ranch, which is on Jupiter or thereabouts. 
Same episode also featured Jane doing an aerobics workout that involved flexing her index finger over and over again. 
I don’t know about the stilts, but I DO know what* Eep Op Ork Ah Ah* means.
Oh, christ. Please don’t do that. Not that earworm again!
I cast Let the sun shine in, performed by Pebbles and Bam Bam. Take that!
The dinosaur explanation is close: the ground was where birds walked
The Jetson’s movie showed a significant smog layer. However the original show showed the ground a couple of times- it was inhabited by birds and hoboes. And they showed a surveyor measuring the height of a building by dropping a plumb line, and then announcing that the building was six inches too tall for the building code. But really, I dunno, it’s just that being up in the sky was “where it’s at”. Heck, they didn’t even really distinguish between the Earth’s atmosphere and outer space,
I have a memory of a random Jetson’s scene where they’re informed to raise their houses again because of the smog. It’s entirely possible that I was stoned at the time though.
That might have been episode #15 (Back to the Present) of Harvey Birdman: Attorney at Law, an Adult Swim cartoon that parodies numerous Hanna Barbera cartoon characters. The Jetson family travels back in time (from the far-future year of 2002 - this episode aired in 2004) to file various lawsuits because in their time, pollution has gotten so bad that they can no longer stilt-lift their house above the rising water levels of the melting ice caps.
George and Wilma were upper class.
Well they were moving on up
moving on up
to the top
moving on up
of a de-lux apartment, in the sky-iii
Does Fred know about this affair?
I do believe that has to be the most obscure Hitch-Hiker’s Guide To The Galaxy reference ever made on this message board.