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.
Yeah of course! Once I went on a buying spree of used WNDR3700. They were so cheap and I won a few too many bids at once.
I gave one to a flatmate when we lived together as students and he took it with when he moved out. Put one in the office room of my current flatmate and still have one or two in reserve. I usually take one with me to LAN-parties.
Before that I once used DD-WRT on a WRT54GL. It also wasn't bad from what I remember.