It's a public server, and a big part of the community are trolls. (Face it) We can not always tell people to do something, or tell someone to stop with something as admins. Because then we would be getting to much in the public "affairs" after all they bought the game, and they reserve with that all rights to do as they want on the Official Server. Of course as long it doesn't inflicts with the server rules. It's perhaps sad for some people, but that's just the way it is. And always was.
What I just said goes for the most points you mentioned, obviously the team hitting/team killing is a job for the admins. However even when there is an admin on, he can't always see the rule breaking offense, therefore we hope that the other public players help us as much as possible by reporting any such offense. In what case we can act quickly on it and deal with the problem. However a lot of times the admins simply don't have a clue if it was on purpose or not. We don't have eyes all over the map.
Sappers are also prevented as much as possible to do somewhat rule breaking offenses, like building objects that get's them to a spot where someone isn't meant to be. However for the part that they close themself in somewhere, I personally would say that they are fully allowed to do that. But when the end of the round is near, they will have to go in to the battle as well to prevent any round delaying. That's when an admin can hop in and do his thing. But that's only when it's a fact that the person is delaying. Therefore breaking the rules.
For some other points you mentioned, like the musicians, people dropping their weapons and running around and people surrendering to the enemy. On all these points we can only do something when it turns into delaying like I just explained at the end of a round. And when it's clear they are delaying. Then we admins can do something.
Last, yes EU1 is getting more empty, and we admins. Are busy with trying to find something to get some fresh wind in the server, and to get people playing more on the official servers again. That might take a while, so in the meanwhile we would highly support you in getting other people on the EU1 server to have some fun gameplay.
However, these points you have noted are not exactly the cases of the sudden dropping of the population. The points you mentioned are (i believe i said it before) happening since back in MM. Though other events lately could have influenced this, like a lot of people quitting NW for the melee system, or whatever other reason. But that's not really important. We just need to find a way to get people interested again. And perhaps the new patch will do the job. Who knows?
Alright my say on it. Hope it helped you a bit.