It's not that the things you say can't be done. Of course they can. But simply buying a product takes a lot of effort away. I've used XMPP messengers and it wo

It's not that the things you say can't be done. Of course they can. 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.