That's not at all what they said. Their actual point was that because Google uses highly custom infra, it is not easy for them to open source or spin off a singular thing. This is valid even if Google's internal infra is strictly worse than what is available openly. Their point has nothing to do with magic infra. It is cost prohibitive to spin off anything because it has to be ported to a completely foreign platform.
> I claim cross-platform porting is not necessarily cost prohibitive, let alone porting from interal APIs to external APIs, and thus their argument is moot.
Yes, you claim this, and you were and continue to be incorrect.
> whenever there is an acquisition, unless it is a pure acquihire, external products get ported into corporate platforms without the world ending
There is a difference between a situation where you are acquiring a thing for $LOTS, and are therefore willing to invest $EXTRA to make it work with your stuff, and the situation where you are divesting from a thing and therefore don't have the same budget.
But even if you reject that: the internal systems are usually more flexible than the external ones (they have to be, they're what the external systems run on top of). And, even when they aren't, "you decided to purchase them" is a really good justification to management, to use your words, to make additional exceptions.
> They are entitled to their own opinion.
But these aren't opinions. You're just factually, demonstrably wrong. Your (now deleted) statement that there may be efforts underway to better align the internal and external infrastructures may be true, but if it is, it just proves the point that the infra isn't the same today, and that as of this moment such a migration would reasonably be cost prohibitive.
To address your other comment:
> You can run an RSS aggregator service without depending on Google's particular monitoring or cluster management infrastructure etc.
Yes, but you can't run an RSS aggregator built to run on Google's infrastructure without either rewriting it or using Google's internal cluster management infra. The useful about having ecosystems like those is that you can couple couple very tightly between infra and application.