I have many nerdy friends who have been Linux users for ages. But most of them don’t know such a thing as Openwrt exists or have never bothered to give it a try. It’s a very fun piece of software to play with and can be extremely useful for routing traffic. Wondering why it isn’t more popular/widely used.
SBCs aren’t routers, while they’re great they might not be good for people who actually want to have WAN and LAN and decent networking performance. Routers usually include some switch chip that will do most of the heavy networking operations, handle VLANs and whatnot without adding CPU load.