Why is the port for the charger on the bottom of the Magic Mouse?

It's on the side of the matching keyboard so it can still be used,

I don't see why the mouse has to become unusable while it charges.

This isn't really a question more so just...something I find really annoying?

Is it possible to trade in my Magic Mouse for another Apple Brand that charges on the USB, can be used while it charges, and has an actual functioning wheel?