> Is it all to support the biggest and baddest high end GPUs that cost more than the rest of the system?

For me, no. I bought a big case, Fractal North XL. It sits on the floor next to my desk so the size really doesn't matter at all to me, except I want it tall enough so that it's convenient to turn on.

It's a nice bonus that building and maintenance is also easier, but it's frankly it's the reaching convenience that matters the most. Could even be a bit larger still.

Nice case! I actually do the same thing, PC lives on the floor next to my desk. I definitely rejected cases that had didn't have the buttons and front I/O on top for that reason.

A small platform to elevate the case off the floor can help lower dust accumulation and may also help it reach the perfect button pushing height for you!