Each episode may not be that great, but the series as a whole can be greater than the sum of its parts.
And like any serialized TV series, you can't really skip episodes without missing key parts of the story, so once you commit to the show you're on the bandwagon.
And given the success of the MCU, it's carved itself a powerful place in popular culture that won't disappear for a long time.
Also, even the Marvel TV shows can be surprisingly high quality (I absolutely loved Loki and Wandavision, but hated Falcon and the Winter Soldier)
There’s a flip side to that, though: once someone is off it’s a lot less likely they’ll jump back on (or even jump on in the first place)
I count myself in that group. I’ve watched Marvel movies here and there (either Thor Ragnarok or Doctor Strange was the most recent) but at this point I’m turned off from watching more because I know there are numerous plot points I won’t get. And I don’t want to commit a week of my life to catching up.
Now don’t get me wrong, clearly Marvel doesn’t need people like me to be an enormous success. But I think it’s a bit of a high wire act that other pretenders to the throne (DC etc) run the risk of failing at.
I'm too old to care about movies much, but that's an interesting point.
I wonder to what extent high-dollar bespoke TV series are hurting the movie business. Streaming and theatres at home were bound to change some habits, but would people prefer to watch a series now rather than a single work?
Personally, I think it's a shame how much movies (a lot them at least) and video games appear to have merged in terms of pacing, volume, general aesthetic, but you can't expect things to always stay the same.
Modern flat panels are so large/cheap that they're a no-brainer in place of most modern theatres. OTOH, the peripheral vision-spanning screens that used to exist were really a spectacle. I remember seeing 'Waterloo' (Rod Steiger) when it came out and that was really something on a giant screen.