I would not say, people absolutely trust corporations.
You can probably ask any stranger o the street if Facebook is trustworthy and they all would say something about FB doing weird stuff with their data.

They all know!
But people have a limit on how many issues they can care about.
We decided that privacy is an issue, others might decide that the issues their sister is facing in life are an issue, or just how to pay the next month's rent.

So, they just use Facebook, google and co. because that is what works, what is there and done. No time to think any further about it!

So, if you wanna get wide adoption for privacy-friendly alternatives, stop solely selling the privacy aspect. The fediverse is great, but all the people who care about the benefits of it are already here. Now try to reach those who don't care that Twitter is a mess, they are just there because all the others are too.
They use it to communicate and not because it is great. The same applies to most other platforms too.
I liked Reddit because it's one platform where you find literally anything! You wanna talk about energy drinks? There is a subreddit.
You wanna know what this thing is you just found on the street? Just post a picture someone definitely knows!