This is because the HTTP protocol is so much overhead that most trackers don't even really run it anymore. I think UDP being promoted to the spec would've been a step in the right direction. Modern trackers have a bunch of tricks like BEP34[0] to avoid getting pounded that would be great if every client conformed to.
I hope I'm not coming off as aggressive. I really appreciate this work and I'm really glad to see a spec revision. It's just as you said, there's been many years and many good improvements that I'd like to see made while there's still a change to break things.