And you didn't understand what I said. While you can not monitor closed source at the code level, you definitely can monitor the apps behaviour. Even the automatic threat protection from the playstore protect function is worth more than the measly amount of people looking through smaller projects codebases.
I hate Google with a passion, but with all their control over android devices, they are more than capable of scanning apps for malicious behaviour and automatically removing them. These few apps in the article are the 0.01% of malicious apps that their algorithm didn't detect.