Core difference:
- Twitter is a broadcast medium and Trump is its biggest celebrity.
- Facebook determines who becomes President.
Twitter also has a massive leadership vacuum given that it has a part-time CEO who isn't even sure if he lives in the USA. Twitter doesn't have a strong boss who will take a stand against Trump hijacking the service, and Trump knows it. Trump is able to smell weakness and chaos like a shark can smell blood.
Every time some junior employee slaps a "fact check" warning on a Trump tweet, while leaving the Trump account active, it makes Trump stronger. If Twitter leadership had any balls the account @realdonaldtrump would be suspended for the duration of the Trump presidency and he should be required to use the @POTUS account. Posts made there are official publications of the Executive Branch with all that that entails.