Convenience and cost for me. You get significantly better hardware for your money than a PC for the same price, while it is guaranteed that all games you can buy will run as the developer intended it. Just turn it on and play.
Exactly. It just works and saves time. Just buy the game, plug it in and play it. Simple.
No 'swap this GPU inside step', 'installing additional drivers step' or 'incompatible hardware errors', or 'run it in 32 bit mode' etc.