Because the majority of the time they are using starter accounts. So even if they get banned, they make another one for free.
Well today my friends I have a solution!
Level restrict chats.
Starter Edition ends at lvl 13, make chats available at lvl 14.
"Congratulations you have reached level 14! Welcome to General chat! To leave General chat or join other channels click on the settings icon."
Or perhaps an easier way would be to make starter editions not have the ability to join chat at all.
At least this way spammers will have to pay $$$ if they want to continue spamming, and when we report we actually help the problem, instead of increasing the workload.
I just though of this while laying in bed, feel free to improve this idea in the comments!