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.
I mean, what does one have to do to replace an ISP owned router and what are the benefits? How much does one have to know in order to setup a connection? How does one get connection details from the ISP owned router? How much does a replacement router cost?
My ISP owned router allows me to configure NAT forwarding, replace the DNS, setup a DMZ, assign static IPs to MACs, turn off the internet at specific times (e.g at night), configure parental controls (allows websites, internet access) per device, and probably a few other things I haven't discovered yet.
For my ISP it's actually cheaper to not use their modem+WiFi router as they charge a monthly lease on the equipment. I declined it and they provided me with a modem for free. All I have to do is plug the modem to my own router and that's it!
The features you listed seems pretty standard to all routers these days.
Most the things you mentioned are barely doable on some of the modern all in one modems where I live.
On mine I've got separate wi-fi networks for inside and guest, I run zenarmor for ads and malicious junk, I run a proxy, I do my DNS on it for all my internal docker instances, and more. I realize I am doing more than your average person, though.