1. Corrupt Management. The money set aside for the development of the club would be shared among leaders and the amount which would have used to pay the players too would be reduced.
2. Nepotism: bringing neighbors, friends children and family members to the football team even though they can't play football.
3. Poor Skillful Coach: When the coach is not good and skillful to train the players and have no clue of selecting players then there will be a problem in that team. And all those factors are faced by many countries football teams.
Definitely right, You said about three main reasons of why Brazil hasn't had good performance recently but don't forget these two factors are what we can see in any country and corrupted management system in the world is what we can see in any country but the fact about Brazil is about their government. Unfortunately, the main reason is their government won't fight with this corruption and instead of that they just keep supporting the people who manage the national team.
That's why I think the main reason for Brazil is having a corrupt government.