I guess different people have different use cases. I am enjoying Mastodon and have had positive interactions with people. I have also found a lot of good quality content there. Additionally, I totally avoid political stuff so haven't had any issues of political stuff messing up my feed. IMO the invite only thing is just increasing attractiveness by creating artificial scarcity.
I think some people are also scared off by the spread-out, volunteer nature of things.
We're betting at least some people (and we only need a small number; we're not greedy) will feel more comfortable with a paid service with an actual company (not launched yet). Won't ever be a large portion of Fediverse users, but I think a broad diversity of options will be what will ensure the Fediverse "wins" in the long run.
I think the invites feature is the only things bluesky really has. At this point, I don't mind as much as the feature allowed me to control who is in my feed and made my feed more intimate like the early days of Facebook. For me, it was a way to weirdly combat parasocial relationships by inviting people I know and talk to.
Theoretically. I can do the same for mastodon. But once I start trying to explain fediverse, they didn't care for it. Fediverse idea is interesting, but loses most people I want to keep in touch with.
One of the things I really like about Mastodon is that I can curate my feed to show only what I am interested in by following hashtags and/or people and muting those people whose posts I don't want to see. There's no hidden algorithm controlling my feed, pushing controversial posts towards me and other stuff. So I don't get why would you need the invite only feature of bluesky control your feed?
Because it is harder to get people I know on board to mastodon than to bluesky. I don't want too many random people on my feed. Most of my feed consists of people I do know and actually interact with. Mastodon doesn't have as much shitposting as I would like and takes awhile for it to get situated to the point I ended not using it. Why bother going to mastodon when I have my friends on bluesky.