I think it's because comics keep refrying the same story over and over again. Boot, let it run, reboot, let it run, reboot ... You get the idea. They try to spice things up and change stuff - the equivalent of remixing a classic song ad infinitum, some iterations will be better than others and you will probably like some more than the original but it's the same song.
Manga and anime have originality on the other hand. Even if some genres become cliche, each story remains a closed entity. Characters here don't end up elsewhere, and once a story is complete it doesn't get a reboot. This means the audience can relate more easily to a franchise, because there are not as many variants, and then move on to the next.
There is also less influence in Manga from current affairs, society and history, whereas comics always meddle with those three just too much. Mangas released in the 80s remain relatable today, but a lot of comics don't for example, or feel like they've aged awkwardly.
So it's easy for people to remain 'loyal' to an anime franchise, but difficult for the average comic.
I know the feels, you are not alone