Why? What does Anthropic have that any other software company that's capable of putting MCP integration in a chat app doesn't?

Nothing, and integration in a chat app would be better served being model agnostic. Anthropic's slack bot here is also at a disadvantage being slack only. 90% of F500 companies are on Teams, not slack. If their only goal is tech companies and startups, fine, but if they intend to grow usage beyond that it needs to be chat app agnostic.