The search function is nice and really appreciated. But, from my experience, the biggest problem with Mastodon is how much work you have to put into curating a feed, something traditional social media has done some of the work for you. I mean it's fairly simple once you get the hang of it, but a lot of people are used to having their hand held.
Also, I'm not looking to piss people off, but I think in terms of the users on the platform it is extremely progressive, and non-progressive people will be less likely to engage with that.