Back in the days of Mark Levinson's ML2 and ML3, the furniture wasn't deep or sturdy enough. And if I lived in earthquake country, I'd want them close to the ground for safety's sake.
My monoblock amps are heavy, and they sit on the feet they came with on the hardwood floor behind my speakers. So, not being on a carpet, they get plenty of air flow for cooling. Just no reason to put them on a shelf.
"There is a very simple reason to put audio equipment on the floor.
Because then you can buy those cute little stands to support the cables, and show that you're a completely committed audiophile......"
Oh, and I don't have any cable risers. But I do consider myself an audiophile. And, as far as committed, I can nominate a few commenters on this thread for that, complete with a ride and a jacket with custom sleeves.