Just like there is cons to being part of a corpo there is also pros. Like you said the extra exposure/followers is one factor but another is the atmosphere, some people (myself included) do better in environments where there is rules set in place and people tell us what to do. Indies have alot of freedom and sometimes that's overwhelming for people. Another is the opportunities, obviously this isnt exclusive to corpos but being part of a big brand will definitely help with things like getting café collabs or voice acting gigs. And finally sometimes people are just fans, just look at Nerissa lmao
(Also this should go without saying but obviously the pros and cons depend per corporation, this is just a general overview)