Any given PC can have one of about 50 configurations each of CPU, GPU, RAM, Motherboard, hard drive space, hard drive speed, plus any number of other things running in the background while a game runs.

The big advantage in that regard that consoles have is that every single one has identical hardware.

An anecdote that can illustrate this: a long time ago I was really into the game Saints Row 2. I have it on PC and played with a couple friends. When playing multiplayer, with one friend our games had weird bugs where his character or mine would seem to teleport around and mission timers didn't work right. Another friend, I didn't have any of these problems with.

It clicked when I realized that the friend I had no problems with had actually helped with my PC build, built his at the same time, and we built functionally the same computer - the only real difference was in hard drives and that wasn't a huge factor. Saints Row was, in its first iteration, an XBox 360 exclusive and SR2 was supposed to be until it got a PC port - as a result, the game had no mechanism built in for how to deal with synchronizing two processors that ran at different clock speeds.