That proprietary software is probably Google Play Services because replacing Play Store is relatively easy. For example, in Russia Yandex wanted to make its own store and in China (where Google is blocked by the government) there are several competing app stores.

Google Play links on websites are not the problem because on Adroid an app can use App Links [1] to start an alternative store instead of opening a Play Store page in a browser.

[1] https://medium.com/@ageitgey/everything-you-need-to-know-abo...