Well it's not common but some people do get those amounts of controllers (though I've got about 5 Xbox 360 controllers, maybe 7 PS4 controllers of various types, plus a racing wheel. 7 Wii controllers). What is considerably more common is people bringing their own controllers for multiplayer games.You never likely considered nor pondered such a thing at all. I game and I sure didn't.
Most people don't play together on the same box regardless. They usually do it online in two different places, which makes the whole notion a bit of a moot point. I also don't think anyone ever goes out and buys 8 controllers for any system.
The idea of a party game with support for 8 people could be fun, but how often is that even going to happen?
Supporting more than 2 would have been a big thing. Considering that Apple systems are *mostly* casual platforms (simple games with short lifespans), theres a huge position there to bring in those party games like the Wii used to have. Again - small, cheap, 2-8 player games. The PS3 has a single BT radio and supports up to 7 controllers via Bluetooth after all.