You're assuming someone has actually told the gate staff what's going on! Most of the time they are kept as much in the dark as the passengers...
Handling agent staff have to wait for instructions from the airline ops department and/or ground staff before they are able to make announcements about delay times and reasons, and as you have noticed, very often by the time they do get any information, it is already out of date!
On both these occasions you were fortunate enough to have access to information direct from the flight deck. Gate staff don't usually have this, and even if they did, might not be able to pass it on until authorised to by someone from the airline concerned. Unless someone actually comes and tells them what is happening, they have to get their updates from a flight information screen on a computer at the gate which only gives a "next information" or "estimated departure" time and a VERY basic reason for the delay.
I agree, passengers should be kept better informed during delays, but this is not always possible if the handling agent staff are not kept updated by the airline!