New Concert Ban

It now seems that there is a blanket ban on all concerts, signed by Rav Elyashiv and many others:

Some points to ponder:

As pointed out by Rabbi Sedley at Life in Israel, this is dated from before Rav Elyashiv is reported as refusing to sign this ban. So what is going on?

The poster speaks about the severe issurim involved. Which issurim are they, exactly?

Are those who insist that one must follow the Gedolim, and that Rav Elyashiv is the Posek Acharon (whatever that means), going to be consistent and insist that people must follow them in this too?

Cynic that I have become, I wonder if it's all a matter of competing interests amongst different askanim.