I think it's a very good example of judging books by their cover; SatAM has a very good intro (though not the greatest by the high standards set by cartoon intros) while AoStH is a much more hastily assembled madcap chase (though it's not terrible). On the surface SatAM looks much cleaner and well made, a serious drama. While AoStH doesn't even have cel shading and has some very weird and misplaced designs.
If you were to just view both shows by flicking through the channels it's not surprising more people, especially in the early '90s when unironic edginess was more prevalent. However when you really sit down and watch both shows, you find that SatAM has all the hallmarks of a DiC action cartoon, silly jokes, bad characters, and just about passable animation. It's not a bad show, but it's basically just the passing grade required for a children's action cartoon. Sometimes it shines, but it's certainly not this dark, serious and mature cartoon like people make it out to be.
AoStH on the other hand is an uneven experience, some episodes and jokes land while others don't. However there is a weird charm to the whole thing; Robotnik is legitimately fun to watch, Sonic and Tails have a cute brotherly relationship, and the visuals have this really unique look to them which make it compelling. Even at it's worst the show is weird enough that you keep on watching to see what they'll pull next. It's also not just dumb slapstick or lolsorandom humour either.
I won't say AoStH is a great show, but I will say it does succeed at being a comedy show more than SatAM does at being a drama. Personally I think a lot of the love for both shows comes from the vision they gave to Sonic, a serious version and a cartoony version. As it is, in this day and age more people are gravitating to silly cartoon shows and slice of life stuff, so AoStH is in the right zeitgeist.