Classic servers appeal to a niche demographic, most people playing classic are older. Likely came back after not playing since wrath or what not. They have no time to be assholes like they were as teenagers. Your reputation matters a lot when you have to run into people you’ve fucked over all the time. Transferring to other realms is not an option last time I played.
Classic players remember stuff like militant raid leaders, ninja looters, and everybody being really bad at the game. People for the most part have chilled out, they know all the encounters having played on private Vanilla servers for a decade, no reason to scream about more DOTs.
Some assholery has happened in Classic when Blizzard introduced honor causing some realms to turn into apocalyptic hell scapes. PvP is kept to battle grounds now, and some servers could transfer because of low faction population. It’s not fun to world PvP when you outnumber the opposite faction 99/1.