That lasted about a season or so, and then all of a sudden they gave them all actual careers. Because, you know, there's a huge market for 20-year-olds without degrees or experience in the Los Angeles business scene.
At that point, they had 2 problems: Party of Five had taken over the teen-angst evening viewers and Melrose Place still had the market cornered on the young adult nighttime soap audience. (And Buffy the Vampire Slayer was starting to take off). 90210 didn't really have a direction anymore.