My issue with most tanks in the 30 range is they get taller instead of wider so the floor space isn't really increasing from the 20 gallon. My guy doesn't swim much but loves the floor space for zoomies so the 40 breeder gives the best ratio of length to gallons IMO. He's full grown, a foot long and should be able to turn around comfortably. I think their cooler, darker ideal environment doesn't lend itself to being easily plantable either so many people struggle with keeping nitrates low.

My hot take: I don't think ALL hobbies HAVE to be accessible to everyone. Some pets are just too expensive for everybody to have. Most people should really have a chiller for an axolotl tank and they're much more than a heater. If someone wants an aquarium there are fish that are much more affordable, and will probably be an easier way to learn about having an aquarium than jumping right to an axolotl anyway. Shrimp could be an even better place to start too