There are a few reasons why I don't talk much when doing dungeons:

1. I watch a video on my second screen
2. I queued with a friend and we're chatting on TS
3. It's more likley to never see the other ppl again then them being from my server
4. sometimes I'm not in the mood to talk

Overall SE doesn't encourage to get to know other ppl in dungeons and there is no cross-server friendlist yet ...

And since I do Expert Roulette more or less on a daily basis I'm glad when it's over.