Why not to lower a threshold to 51%?
If we don't find an anonymous mainer, this process can take years.
Then everyone has to upgrade again, including all exchanges and miners. It's only been a few weeks, and probably the cost to rent hash is not really prohibitively high since entire signaling period are only a day or three.
Also old wallets could fork to follow a different (non-upgraded) chain temporarily which would be bad for consensus.