when a team gets relegated the salary of the players remains the same while the funds from tickets and sponsorship decreases so a relegated team may end up losing money in the next season. Also players will get less training points because of the lower league.

Let's say the money could be recuperated second season after relegation if the team qualifies for CL and advances in the higher stages but still overall team worth would be quite equal to the case in which they would have stayed in the superior league.

The current system with no relegation favors persons who leave the game for a certain amount of time and then come back
The relegation system would make the leagues more balanced but maybe a little too difficult at lvl 1-2