So have I, but if the router has to be reset or replaced, all the reservations (not just the U1) will need setting up again. So much simpler to have user control over networking in the device, as several other of my devices do.
It’s not a simple task in the router either (YMMV). I would not be able to do it unless the U1 was connected at the time, then it needs to be identified in the devices list (not difficult with the U1 as it identifies itself as “U1”), and then register its MAC as having a reserved address.
I would not have bothered had my U1 started out on .118 (which I got used to) and then one day randomly switched to .108.
I’m all about user choice. It doesn’t seem hard to provide the option of manual control over the networking parameters.