It doesn't need to be but it is. What are you gonna do, bloat the case just to fit an Ethernet adapter? Also, what's wrong with it being in the charger? This is actually genius, this way only a single cable leads to the machine itself.
Jokes aside, putting the connection on the power brick actually seems like a really smart idea for cable management under the desk. And, you will have one fewer cable plugging into the back.
It's an aesthetic win since you don't need the cable coming out the back of the machine and it's a pragmatic win since cable management is much easier if it can plug into the power brick that's already on the ground.
It's an almost ridiculously portable stationary device
Power bricks are the most inelegant solution to a problem ever. Can’t think of a clever design to accommodate the features we want? shove it on a box and put it to the side. Lazy.
And wasn’t the M1 supposed to be so efficient minimal cooling and power were required?