It is not as easy as you think.

Take Slack.

Atlassian failed to compete with its Stride alternative and cooperated with Slack instead.

Microsoft Teams maybe a more viable alternative, but it's still less user friendly than Slack and it is remain to be seen who will win.

Money does not decide everything, you have to un-burden a department or run internal startup. This is hard and too few companies are doing it in a good way (Valve?).