I can and I will call a/c every time I NEED (to provide safety of course). If pilots are really busy, performing some actions, they can just ignore my message
Hmmmmm..... are you one of those guys that insists on giving taxy instructions to a/c whose wheels have JUST touched the runway, I wonder?
While I do agree that we need to know the reason for a go around, everything has it's time and place - let the guys get out of whatever trouble they may be in before you start to badger them for non-urgent information. If you feel you can't let the next one make the approach without said info, then a) break them off or b) give them the info you DO have (eg preceeding went around, reason unkown) and let them make their own decision - it's what they're paid to do.