The reason Berman and Braga get all the blame is we know their names. Do we know the names of any of UPN execs ? I certainly do not. So its easy to lay all responsibility for things fans do not like on the public face of TPTB. Which for television is writers and producers. Even if its not the reality.
This is not unique to Star Trek either. On any show that takes a turn the fans do not approve the known Producer is demonized. Being ignorant about how network tv works.
I know all the various DC Comics tv shows had a lot of different groups having a say in the content. Of course DC Comics itself. Plus Warner Bros, sure they are owned by the same corporation but they are still separate companies with different people working at each. On top of which you have the network which the show is airing on.