Because they breaching the common rule? Or being a spam account? Being reactionary is usually not a ban-able offence, and we admin isn't here to control and fine tune how everyone act to a specific way.
I mean, if you or any other admin want to do that, feel free, but i ain't got time for that, and i trust you adult for solving common conflict yourself.
They called to violence and insulted our members several times in the first thread linked in the OP https://jlai.lu/post/11504685
If Jlailu members had done the same on another instance's meta community we would have acted on it.
I see where you come from, we don't monitor everything that our members do, but this was a large scale event with dozens of people taking part and 248 comments.