The benefit of signing the first time (and with the new addresses) is that it proves that you actually control those addresses. That might be useful, but it does not prove identity.
What's the benefit of knowing that I actually control an address the time I stake it? You have two options.
Option 1: Post an address you own.
Option 2: Post an address you don't own.
Whichever option you choose, you deserve your fate. If you chose option 1, you'll be able to provide a proof of your identity in the future. If you chose option 2, you'll only harm yourself.
There might be a good reason to prove that you control an address upfront. I don't know a reason off-hand, but if you are going to stake and address, you might as well take the opportunity to prove that you control it.
It seems that they don't get this since the 20th post.
Another suggestion, I might be wrong though.
If you just put Bitcoin address or PGP key, it is easy to impose another person. A signed message is better.
I don't fault them. Signatures and their capabilities are complicated.