Why would that matter? Certainly, important to know the why, but more important is the outcome. "Who are you selling to?" and "Who has the spend/budget?" are most important. Tragic, for sure.
If Teams is problematic enough, and enough upper-middle folks who have to use it are unhappy and want more productive tools, the guys with the spending power may decide otherwise. Salaries are a far bigger expense than chat software licenses; wasting 1% of time of 50 highest-paid employees would tip the scale on numbers alone.
"You don't get it Steve, that doesn't matter." [1]
That actually does not matter if Teams is making larger progress than Slack. I prefer Slack over Teams too, but to disregard the market force and market position of Teams is naive.