I can't be bothered to read the thread entirely - so this most likely has already been said
But to answer the OP's question:
The addition of the WotLK Group Finder tool was one of the first steps that many people consider as the start of WoW's downtrend in playerbase. It definitely contributed to the servers feeling much smaller and mattering less, as you no longer needed to rely on just your server in order to get things done. You didn't even need a guild anymore to see content. It started to diminish WoW's social experience, which seems to be something the people in charge of Classic are trying to avoid.
Its not a hatred for the tool itself, but what happened as a side effect of when it was originally implemented.