Once they decided to make the mouse chargeable it was inevitable the plug would go underneath. A plug that allowed you to continue to use the mouse wouldn't stand up to the stress and strain of being dragged around your desk.
It's the Lightning connector which was never designed to be moved within the socket tens of thousands of times a day.
Plugs not being able to stand up the stress and strain were never Apple's concern.
Apple cables (for lighting, charing MBPs, etc) have easily strained since time immemorial.
I am consistently annoyed when Apple, who has the magnetic charging plug patent until 2025, refuses to use it in exactly the applications where it would be most beneficial.