Jester David
Hero
This is especially true with WotC farming their adventure storylines to second parties like Sasquatch games and Green Ronin. There's maybe three or four publishers that can do that currently and they can't make a storyline back-2-back. There will come a time when one company is busy with the current storyline and the go-to staff at other publishers are busy with other projects. And WotC has to choose between putting the storyline on hold, giving it to an overworked studio, or risking a really untested company. I like Goodman Games (and have given them hundreds of dollars) but it's uncertain if they have staff and expertise to do a full colour product at the standards WotC expects.3) More people with system mastery. This one was told to me by someone at Wizards. Compatible publishers are a training ground for new developers. You need experience to get better. And writing for that compatible publisher means that Wizards can hire people that are already experienced with the system, a level of experience they would not otherwise have. Sure, someone can be good writing for their home game about stuff they like, but when you have to write 10 magic items under a theme you had not thought of before all on a deadline, you learn more.
More 3rd Parties means more companies that *might* be able to move to the big leagues and more staff for the existing publishers.