You can say the same about running Linux on your laptop. The answer is that you don't buy the random $20 routerat Walmart and hope that you can install openwrt on it. Instead, you buy the router specifically to install openwrt on it. It's certainly a bit more painful but you get used to the idea of using a bit older gen hardware but enjoy excellent software supoort.

Over time, with enough people do it, the manufacturer will realize that and cater to you (see the Linksys 54gl router, archer c7, dell laptops, and Lenovo Thinkpad -- the manufacturer all know people buy the hardware to run the software they want)