I could. That requires me to have a 3D printer and be willing to invest the time in figuring out how to make a case. I don't, and I'm not.
Of course it's going to be more flexible, just like it's more flexible to design your own device from scratch. But I'd trade that flexibility away for more time to do things I actually want to be doing any time, and I'd be willing to pay quite a bit of money to get that kind of flexibility without having to spend as much time on it.