Could Hilarie never coming back be personal?
Apparently Hilarie was married to assistant director Ian prange and they divorced in 2009, her last season on the show. Ian was the song of executive director Gregory prange.
Could it have been personal for why they didn't bring her back and also didn't ask? I get the feeling that's the case while rewatching the series because the later seasons take a lot of jabs at her for leaving. They mention how her friendship with Brooke faded and how Brooke was always there for her but when she needed Peyton she just left. And CMM made an appearance but she did not.
I kind of feel it may have been personal. Maybe she was having an affair as her and Jeffrey Morgan got together that same year following the divorce.