it's not that bad imo, it just gained hate through the years thanks to the fandom. i'm not saying is the best anime ever, but it isn't the most awful thing they make it out to be.

that's talking in general. when it comes to more popular than othe GUNDAM series, it basically comes down to exposition. GW was put on tv in the 90s when anime was starting to be a thing, before that, it was that mecha series guys liked and hell, many people didn't even know about how old and classic it was, internet was also starting. but the general public started to pay more attention to gundam after that. seed was pretty big too.