It is easier and more convenient for players to have a GM "there and then" I agree, but really not easy for the GM team.
Having an online gm at all time requires to have either a very large team or highly active staff members, you also need to set up a schedule to make sure a GM is on duty at all time, and while players aren't asking anything or having problem, then what happens? the gm is bored i guess, but they can't go afk otherwise it defeats the purpose. We have to remember that GM are unpaid on most servers, so even if it's technically possible to have a gm online at all time to handle that kind of report, it's not very practical and most likely a bit boring and you end up having staff quitting.
The bigger the server the more doable and worth while this would seem to be, but small/medium servers really are unlikely to be able to provide that kind of 24/7 service.