Are there companies who self-host their chat and project management? Pretty sure there are. In the end, that's why slack is has a free option that works well for small teams that do not need to keep old messages.
But simply buying a product takes a lot of effort away. I've used XMPP messengers and it worked. But I'm a tech savy person. If you have colleagues who aren't then you need someone to support them in installing the client, setting up everything, etc.
With solutions like Slack there is a lot less friction. People know how to use it in a browser. People know how to install the client.
You pay for the convenience of the product, no necessarily for the features themselves.
Plus its almost NEVER up to the tech people to deploy whatever they want, someone at the C level got a sales pitch for a given product, liked it (may have even gotten commission or a kickback) and told you to install, setup, support given product(s). or in my situation Infosec told the network guys to implement X and it breaks everything at the user level...
and your end users will hate you if you reinvent the wheel for every internal product/process... things like Jira put a ton of that kind of thing into one interface, under one user - preferably with single sign on.
your v1.0 of a given product will never be as easy to use, or well thought out as v10 of another vendor's product doing the same thing.
And those companies take care of regulations, scalability, and can even help with audit findings - not to mention gives you someone to blame when things hit the fan.
I’ll grant you Dropbox.
I mean we all at some point look at our personal subscriptions and go why the fuck am I still paying for Netflix, I don’t even use it. But we never seem to consider that it takes less than hour to set up a simple chat server or install and open source PM solution.