To be fair it mostly looks that way because ARM has ruled the market for at least a decade, and there's just so many of them. But yes, many vendors make no effo

To be fair it mostly looks that way because ARM has ruled the market for at least a decade, and there's just so many of them. But yes, many vendors make no effort to mainline their code. But some do, or pay those samaritans to, and as a result you can definitely get boards (including this kind of 5-port switches) that run completely supported on a mainline kernel. My home gateway is a Turris Omnia, supported in mainline for years. I run a plain Debian on it, works great.