Too bad nobody directly addressed your question as to whether it had anything to do with pauses which would be unbearable on the gamer's experience.

Perhaps the question is still open whether properly managing allocation, using object pools as well as other strategies would enable writing triple A games with a managed language.

Or perhaps all we need is a GC race (à la JS engine race we've seen in the major browser) which Google might very well be starting with the recent efforts on the Go garbage collector.