They refused to respond to an Australian government investigation. (Because Elon fired the two people who interfaced with Australia.)
The fine is not directly because they haven’t cracked down*, but because they couldn’t competently answer if they’re handling it at all.
(* and they’ve probably fired enough trust and safety people that they’re also having trouble there, but that’s not exactly what the fine is for.)
If there’s one issue, ever, that you should be at least a little “both sides” on, it’s this one.
There’s no way you can honestly argue only one side of this.