I tried to go to a meeting

yesterday. 
Now I will admit I was late. That was unavoidable. I would have been there on time but there was an accident on the road and that meant I had to do a detour and, because of the detour, I had to wait for a train to pass through. As I only ever have just enough time to get there it's a problem I have faced before.
Normally I can prowl in quietly and not be disruptive. There is a back door to the hall and a front door. If I am lucky the back door will be open and there will be almost no disruption. The front door will usually be closed against the traffic noise from the street but a quiet knock on the door will usually get someone in. 
Yesterday the back door was shut. The person who usually has it open was, for once, sitting inside. (He comes but doesn't usually sit in the meeting.) I tried the front door and nobody answered it although I knew there would be people on "door duty". I tried several times. I tried to knock as cars were not passing and nobody answered.
I ended up waiting outside for more than twenty minutes waiting for the formal part of the meeting to finish. If it had not been for the fact that I had promised to deliver something to someone at the meeting I would have been tempted just to leave.
Even when the formal meeting was over and I could bang rather more loudly on the door it was some minutes before anyone answered it. I didn't say anything to the person who answered the door. I let the Secretary know later - by email. I was in no mood to confront her and it wasn't her fault anyway.
The answer would be to have the back door open for late comers. It would not be a security issue. There is nothing of any value in the tiny passage which leads into the hall and anyone going into the kitchen would be seen - and are thieves really going to wander off with the  urn?
All this makes me feel irritated and scratchy. It takes me half an hour to pedal to the meeting and a little more to get home. Other people simply get into their cars. Some even get picked up by other people. One or two catch a bus but, for most, it's a matter of a car journey. They aren't out in the weather. Yesterday the weather was pleasant enough but there have been times when I have pedalled in the heat or the cold and rain.
The other annoying thing of course is that there are now things I do not know about . The person who would be most likely to make sure I knew these things was not there. I should have been able to tell her instead.
Would it be that hard to make sure people who are unavoidably late could actually get in?