I speculate that having this open source increases its popularity, which makes more likely that any given potential hire or VFX company will have experience with it, which makes it easier for DreamWorks to ramp up new hires or contract out to third party companies.
When I was at EA, we switched from a proprietary UI tool (which was quite well suited for consoles) to Flash (which wasn't) entirely because it eased staffing problems even though the technology itself was a worse fit. The best tool is often the one that people you can hire already know.