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)