You could also use ***[fixated][1]***:

> def 3: (*Psychoanalysis*) to develop a fixation; suffer an arrest in one's emotional or sexual development.

> Fixation, n.  
> def 5: a preoccupation with one subject, issue, etc.; obsession  
><sub>*definitions from [dictionary.com][1]*</sub>

Normally this takes *on* as its preposition, so your example would be

> The mainstream media are fixated on reporting gossip about politicians and celebrities.


  [1]: https://www.dictionary.com/browse/fixation