It’s likely there’s a pretty simple answer for this rather than it being about purity of design: the mouse has to click.

There’s an actual motion that needs to take place, which means that the top shell of the mouse has to move up and down. Since the top shell is nearly flush with the base, there’s really not a part of the surface that won’t move when clicked.

Integrating the Lightning cable port into the front of the mouse would have made clicking actually impossible. One solution would have been to provide a fixed port on the front with a gap large enough to accommodate the float of the click, but I’m pretty sure it’d have been pretty unsightly.

One last thing to mention is the size of the inside of the port itself. Considering the bulk, there’s really no elegant way this could have integrated into the front except to reduce the click surface and increase the base to accommodate the port.