Why do most power supplies have power cables connected to it?

[froggyboy604]

I'm guesing pewer supplys mostly have power cables connected to it because it prevents the user from not pluging in the power cable the wrong way on the power supply end. Plus, it prevents damage cables from being reused when installing a new PSU.

But, these days there are modular power supplys which seem like a better idea since it reduces clutter, improve airflow cooling, and makes removing the power supplies or cables easier.