I would suggest that the reason development teams often don't go to open testing is that it is not really very valuable for game development, because being a player is not being a tester:
- Most players do not test bugs in a methodical manner
- Most players do not provide bug reports in a structured manner
- Many players do not understand what an "alpha" or "beta" version is and are quite happy to write huge rant-posts about the beta version they just downloaded because their friend told them to
- Or in our context, about how DT have porked their favourite ride deliberately
As a result, even confirming bug reports takes far more time than with dedicated testers because players will not necessarily check basic facts such as whether they can reproduce a bug, or even note down the specific conditions in which they experienced a bug. It's not really worth it just to satisfy players' desire to get a new version early.