I am increasingly convinced they are trying to direct traffic to apps that use their Ads network under the guise of such vaguely-about-security messages.
If you download an App using MSFT Edge on Windows, it will warn you (MoTW). If you download an App using any browser on macOS, it will warn you (also MoTW). But if you grab apps via the App Store, there's no warning.
Is that also unfair?
While it's been many years since I did hands on end user support, or even worse, support for family friends back in the 9x days, people still have little clue about what they're doing without a big flashing warning sitting in front of them..., which even that sometimes does not work.
Even I'll often choose an extension for Firefox that has more installs. If I'm going to get a SAML decoder, I want the least phishy SAML decoder available.
Play Store isn't a web browser.
Play Store is NOT a web browser. It downloads from one place and one place only.
Those warnings in the Store aren't meant for you or I.
https://chromewebstore.google.com/search/ublock
As a user who suddenly knows nothing about uBlock the ad blocker, are you going to trust an addin with 2k installs and 4.3 stars, or an addin with 30m installs and 4.7 stars?
Install base can be informative when choosing.... anything, really. In many people's minds something that is used more is better in some metric, be it performance, reliability, price, et. al.
EDIT: My numbers were way off :-)