EDIT: Added source from where I read it.

~~From some other comment I read,~~ it apparently was due to google paying companies to set Google's stuff as their default. Something Apple does not (have to) do.

This comment by AnalogyBreaker on the article seems to explain it pretty well:

The "this doesn't make sense" crowd are missing the point. Android is open source, anyone can use it. Google licensed it that way to spur adoption and (in theory) not solely be responsible for its development. They could make their own closed OS, kept it exclusive to Pixel phones and have a closed app store... but we can can all guess how well that would have went... not well. So the open source route makes sense.

Because Android is freely licensed to anyone, there is a market for apps that Google theoretically doesn't control and resides on non-google produced devices. They do control Play Services, however. That's not open source and includes proprietary apps basically essential for an operating smart phone such as Google sign in, Maps, and of course the Play Store. Google used their market dominance in those fields to prevent third parties from launching or installing competitors to the Play Store by denying Play Services to those who didn't comply; paying them off directly or brokering sweetheart deals. That's appears like an obvious abuse of their market position.

If Google wanted to be treated the same as Apple, they'd have to develop phones the same way as Apple. They didn't do that, instead they rely on third parties and those third parties have protections from Google abusing their monopoly position against them. To suggest they should be treated the same as Apple is akin to wanting to have your cake and eat it too. For the record, I'm not a fan of the Apple ruling, but there are clear differences between the two cases and seeing different outcomes shouldn't be a surprise.

Source

There was another comparison I read using an example if Microsoft paid stores to not sell PlayStations, but I can't find it anymore.