Every entrepreneur wants to assume the counterfactual that but for their startup dying for reason #6354, it would've lived!
Since the OP refused to provide any further details or answer any questions people sent towards him, I tend to believe it's the latter.
Enshitification ramps up after the competition has been destroyed.
Unless his startup was VC funded and was already seriously penetrating enterprise and then couldn't get round C of financing because their 100+ person sales team couldn't make the high growth math make sense.
Otherwise usually your value prop can't be closely tied to *relatively* minor accounting decisions in the early days or you're already DOA when facing an entrenched opponent whose team can easily undercut you well beyond generic bundling deals (whether via strong existing relationships, making wider non-standard sweetheart deals that wouldn't be under regulatory scrutiny, and marketing budgets).
Don't get me wrong this can harm markets generally, and megacorps should be held to higher scrutiny, but usually it's not that simple.
My best guess is that the pandemic is what happened — if this story is true.
The bundling didn’t matter when no one needed a large amount of seats for an in-office workforce.
But during COVID and currently, there was no better pricing than what Microsoft is offering for all the things (ex. Azure + 0365 + GitHub).
The market shifted from Slack, Zoom and <insert anything else here> to Teams for large enterprises when they recognized that no one was coming back into the office.
Source: I bought enterprise software for a Fortune 20 during COVID until I launched my startup.
Whether a small European startup would have won out locally without Microsofts market position + price advantage idk. But without details I'm not sure the financial decision making of a Fortune 20 matters in this conversation which was part of my point.
Once your sales team is competing on price vs Microsoft it's basically over for young companies. Your value prop has to be much more than that until you're a mature business.
There's degrees to market manipulation and market position where this sort of explanation would hold water as being the root cause of death knell.