Actually, it's really easy. Aside from portability, variation, and availability you mentioned, manga doesn't require you to read other books for a crossover or give the impression that you need to read other books.
There are long runners, but not to the hundreds of issues, where you have to ask first, do I need to read them all and is there's a jumping on point, so even if there's no jumping on point they can catch up pretty quick.
Connected to all of that, there are no continuity issues since each story's done by 1 writer.
Then for the short runners, you'll get actual character progression, actual character deaths, there are stakes, and they matter. They don't make me look at news of character deaths and say "eh. again? boring"
Sometimes there are retcons, but they're not spread out on different books, so there's no sudden surprise about the return of some other character that happened in a different book that made you go "wait I thought he died"
In short, manga is a lot less bothersome than superhero comics and when it comes for entertainment, people are gonna gravitate to the easier ones
As for colors, a lot of people do prefer anime to manga, so yeah, people do prefer colors. Often they pick up the manga because the anime isn't finished because they have to catch up with the manga and they can't wait.