[foxylion]

But managing an IRC server cluster for 10.000+ users is no simple task.

Paying experts in their field (chat tools in this case) is most of the time the most reliable and cheapest variant. You must also include that Slack has plenty of features that are not available in IRC and mean the productivity is not as good.

[jbverschoor]

Since when is running any service for a number of people something people compare with running google?

30 years ago, efnet was (apparently) 35k users.