No, the logic is based on precedent. In the case of the Zenimax acquisition its a publisher that formerly was multi-platform, and as such its valuation was based on the revenues of a multi-platform operation. A change in business plan as drastic as dropping future support for other console platforms is certain to impact turnover negatively in the short to medium term.
By getting ownership of Zenimax, MS put themselves in a position to be able to pick and choose the path ahead. We already have an example with Mojang of a scenario where they chose not to change the publishing model drastically, just shape it in a way that made sense to them. Leaping to the assumption that they'd definitely opt for exclusivity with Zenimax just was a bit of fanboy wish-fulfilment because it was no more or less likely than them taking a business-as-usual or some sort of mixed strategy in the short term based on precedent.
Evidently they've judged that taking the short-term hit is justified for the long-term benefit of their platform. Which is perfectly reasonable, as is the careful way that they are suggesting that exceptions may be made in future if they deem it strategically worthwhile to do so.
Its basic owner's prerogative.
First your assuming they valued the brand off of the muli-plat operation and not the value of the IPs themselves (which makes more sense if they are taking ownership).
Second, developers aren't going to mass quit because they have to work less, reducing a console platform literally means he devs can focus on two platforms instead of three, so more resources are readily available.
I'm not aware of any business, that makes a purchase without doing the math to account for the return on their investment, and how long it will take. I'm very positive MS did not consider losing 30% of sales to a competing platform when doing their revenue forecast.
Mojang is a poor comparison to this as Mojan had 1 IP that was Minecraft and the game was already available on various platforms, the only example Mojang can prove is that MS isn't going to remove support for existing platforms that the IP has already launched on. Another reference to this is MS honoring the 1year exclusivity deals made before the purchase. Also, Minecraft dungeons could be an example, but they don't even attach the Xbox branding to Minecraft, they have left it to operate on its own. The Bethesda deal had a big ass XBox logo right next to it.
There is no history to use as an example for this purchase, so Phil's words have to be taken directly in context to predict the future, and we know 2 things he has said that is relevant.
1. They can make their return without needing competing platforms user base
2. They will honor existing deals, but future games are case by case
You can put them together and realize he isn't supporting anything other than Xbox/PC/Gamepass, and if they launch a game on the PS5 there must be a very specific reason why (Gaas/Low budget game for high return, idk?)