The cost of the boat sinking is also very high and that’s looking like the more likely scenario. Watching your competitors sink huge amounts of capital into a probably sinking boat is a valid strategy. The growth path they were already on was fine no?
_Number would not go up sufficiently steeply_, would be the major concern, not collapse. Microsoft might end up valued as (whisper it) a normal mature stable company. That would be something like a quarter to a half what it's currently valued. For someone paid mostly in options, this is clearly a problem (and people at the top in these companies mostly _are_ compensated with options, not RSUs; if the stock price halves, they get _nothing_).
The cost of missing that opportunity is why they're heavily investing in AI, they don't want to miss the boat if there's going to be one.
And what else would they do? What's the other growth path?