I don't use or even like Slack, but what is the problem with that?

I mean they are already giving you the oppportunity to use a limited version for free, you can't expect them to give you one of the most useful features imho when you are just using their resources and infrastructure in exchange for nothing; it doesn't make any business sense.

If I'm a non-paying user of Slack (or whatever other SaaS with a free tier) I am not entitled to anything whatsoever, I'd be grateful for the fact that they allow me partial functionality at all.