> Maybe all of the low hanging startup fruit of that variety has been plucked.

I felt that I agreed, but then I would have equally agreed right before Slack got so popular, so ... maybe not? We often don't see the long hanging fruit until it gets plucked.

Or rather, it's not as low hanging - just that the difficulty is not technical, it's that building something nice that works well together is just not easy, regardless of the vertical.