Actually, there isn't. It's perfectly possible to be able to have a process to request bootloader unlocks from Apple, and also be able to use the ecosystem.

The entire point of the saying that you can't have your cake and eat it too is that, well, it can't be both in your hands and in your stomach. But it's perfectly possible for me to be able to call Apple and get a bootloader unlock code, without any other change to anything.

The general point behind the proverb boils down to "you can't have it both ways" or "you can't have the best of two worlds".

That's essentially what the parent comment is trying to do. When offered the Android ecosystem as an alternative, the counterpoint was to lament the lack of Apple Watch and iMessage support in the Android ecosystem.

This is textbook "I want it both ways".

While it's literally impossible to have cake and to have eaten it, it's not impossible to have a good phone and a hackable one, in a single device.

The cake thing was in response to you wanting Apple Watch and iMessage…on Android.

This is the definition of wanting it both ways.

I don’t think anyone would argue that it’s technically impossible, but that should not be mistaken with “practically impossible” given Apple’s business model.

I don't want iMessage on Android, I want a hackable phone that supports iMessage too. I realize that's not really possible now, but it's not a logical impossibility, like being alive and dead at the same time.