Social media challenges
The Network Effect
The main challenge with moving away from Big Tech social media platforms is the network effect. You're there because everyone else is there. If you move and they don't... then it's not useful.
The way to overcome this is to move away slowly in small groups, for specific purposes.
Ecosystem thinking
Another challenge to moving to better social media is ecosytem thinking. This is where you think "I need to have everything under one roof". This is a barrier to leaving Facebook in particular. It has messaging, a social feed, photos and groups all in one platform.
Just apply the 'don't put all your eggs in one basket' maxim, and you can get away from ecosystem thinking. You can find specialist apps for each functionality you need, and they can connect if they are decentralised (e.g. federated apps in the 'fediverse').
Anti-democratic
As Jamie Susskind states in his book The Digital Republic, big tech social media is set up as "a privatised system of discourse that operates between consumers rather than citizens, according to merchantile rather than democratic norms".
In other words the values and principles guiding social media platforms are commercial rather than democratic. The platforms prioritize profit and market logic over public interest, equality, or the free exchange of ideas.
So now you know: on those platforms you're being
1. surveilled and played for advertising cash
2. constantly manipulated by their algorithms