Okay so everyone's saying popularity and money but I guess you wanna know how stuff gets popular.

Stuff that breaks the general trend is normally remembered for being so different. Rakugo is well on the way to becoming a cult classic for breaking away from normal anime trends and being an excellent drama on its own.

Meanwhile we have things like Cowboy Bebop which is an older classic, it's likely Bebop gained most of its popularity by airing a lot back in the 90s and early 2000s, show was good enough to stand on its own and word spreads. I think a lot of the reason Bebop is popular in the West is because the premise and characters very much appeal to a western audience. I don't know for certain but I don't think it sold very well in Japan.

We see things like K-On! as well, in Japan people found K-On! to be highly relateable. A lot of us in the west think the show is very cute and so enjoy it for that but the show got massive sales in Japan because of how relateable some of the aspects of the show are. It also experienced very high female and non anime fan viewership further emphasising how well it was marketed to everybody.

With Shonen series like One Piece and Naruto... To be perfectly honest I'm convinced that the game in Weekly Shonen Jump is executing the same stuff better than the guy before you. The top Jump manga is always extremely similar. While things like BnHA is amazing I don't think it does anything new, and it tells a lot for WSJ. Yet their all really hyped and crazy and we all watch them anyway because it's well done. I suppose ultimately everyone just wants a show to be made well....

There is no single thing a show can do to make it a classic or culture icon other than perhaps be made exceptionally well. However there are a couple of minor things that contribute. I have probably mentioned 7% of all these factors.....