[itp]

There's also the ability to collaborate with people who don't have an iOS device. If someone creates a Collection in Apple Maps I just don't get to participate. If someone creates a shared list in Google Maps I can see it on my phone, a web browser, someone with an iPhone...

[briandear]

And Google gets to see it too. And all their advertisers.

[reissbaker]

Google doesn't give your map collections to advertisers.

It's true that Google gets to see them, but Apple is no better in that regard: they store your collections on their servers too (where else would they store them?).