Actually, I prefer Joao Felix to stay at Barcelona rather than move to Chelsea and then move to Milan. Joao Felix had a good season with Barcelona, but Barcelona was unable to make him permanent due to poor financial conditions. Now Joao Felix has joined Milan and is continuing his professional career, but now he is like an outcast.
His performance in Barcelona wasn't very satisfying. It was the main reason that Barcelona didn't try to sign him permanently. So, there was no chance to stay in Barcelona at that time. Unfortunately, Atletico Madrid didn't include him in the main lineup. In this situation, Chelsea offered him to join, so Felix has no other choice. However, it is a good decision to join AC Milan because AC Milan needs more potential attackers.
I don't know what is stopping many clubs from making him permanent and giving him lots of opportunities. Basically he is a good player with a good game, but he is difficult to find a club that really needs him. At Barcelona Felix made 41 appearances and recorded 10 goals and 4 assists, but the lack of opportunities at Chelsea may mean he has to leave.
The reason is only about the performance. As I said, his performance didn't satisfy the clubs, so they never signed him permanently. Anyway, 41 appearances with 10 goals and 4 assists aren't impressive stats. It is very clear that the clubs didn't see a big potential in Felix. But Felix is quite lucky that AC Milan wants to take him as a loan player.