Jeri Ryan on Star trek Voyager quickly used her influence over Executive producer B. Barga, her boyfriend at the time to make the show about her.
I have to say that adding her to the show was unnecessary after Kes departed, she didn't not bring anything to the show that couldn't have been done without her. (The enemies that faced, The Borg, etc… Like the Wesley Crusher and Tasha Yar characters, she was just not needed.
Anyone who seen the show know the seasons 5 and 6 almost every episode was about her and the Borg.
And most were just some of the worst episodes.
By the end of the 6 season it's said that Jeri Ryan was not on speaking terms with most of the actors, (Garnet Wang most of all, who was the most outspoken about Jeri and why his character really never improved much), but Robert Picardo and Robert Beltran. If you watch the show again you'll see that by the 6 season most of her line and interaction are with the Doctor (Picardo) or Robert Beltran (Chakotay).
She had indirect line with the rest most of the time, over the com or third person talks with the others. Picardo and Beltran the only ones on speaking terms with Ryan felt that the show was becoming too much about her and why seasons 5 and 6 were just the worst.
This is why Season 7 when the show ratings were going up, it ended suddenly. It's said that many of the other actors would only do a few more season, if they kill off Jeri Ryan character.
The writers and Producers (her boyfriend at the time) decided they'll end it.