This is not "stupid" design. There was a deliberate decision to make the mouse useless while charging. But why?

Perhaps you're annoyed that you have to pause your work and let it charge, so you'll buy another one as a backup.

Also, if you own one long enough, eventually its internal battery will deteriorate, offering progressively shorter work time. If it had the chargeing port in the front, you could leave it always attached and still use it, just downgrading your wireless mouse to a wired mouse. It would be acceptable to some people. But this way you have to buy a new one.

Those are two potential chances for additional revenue with just one seemingly "stupid" design choice.

It's the same as putting critical components next to heat sources in their laptops. Apple doesn't do stupid things; it does asshole things.