"Why did the community spent years on marketing & improving Steem, just for the useless founder to get a nice payday?"
The platform was always designed for that purpose. It was obvious.
If this was about attracting users with a well designed platform meant for user experience, the issues would have been addressed back in 2018 when these issues became undeniable.
Remember when the whole game was buying votes from bots?
Don't worry, Justin has an excellent track record of making good profits while sucking the life out of his investments.
So Justin Sun is gonna do exit scam with Steem/Steemit... Hoard as many coins as possible and then dump all of them on exchange and convert to other cryptocurrencies or cash out... Before rest of the users can cash out, he contacts exchanges and asks them to stop Steem deposits and withdrawals and only allow use of the Tron-based Steem token.
Unfortunately, I'm not a mind reader or able to predict the future.
What you're suggesting is not a huge stretch. Consider, only about 0.000035% of users are whales (was using older numbers I found, but most recent results I could find, but less than 40 users).
The main point was that the platform was always about making profits, more than creating a platform that could attract users and fulfill on the promise of what the platform could deliver. If I was wrong, the usability issues would have been addressed, the issues of manipulating the system would have been blocked, and the focus of expansion would have been on improving systems deepening the functionality instead of spreading wide across a series of 'dapps' most of which are varying degrees of functional.
The results are pretty clear (when we can find metrics) that the platform has been on a downward spiral, fewer users, fewer comments, fewer posts, fewer rewards. I feel bad for anyone who is more invested in the platform than as a free hosting service for a blog.
I think Justin Sun and Donald Trump are a lot like... Both are business men that try to run the world like it's a yet another corporation.