It also only solves that very specific problem. You don't need to side-load an app to scam someone. There's plenty of malware on the play store you can use. And, you don't need malware. There's plenty of legitimate apps you can use for scamming.
And, you don't need an app, I would imagine most scamming is done without an app.
So, really, we're solving a subset of a subset of a subset of a subset of the problem.
yes. Hence, "this isn't about keeping people safe".
The most effective means of hacking is social engineering. You can't solve that with any number of "security measures". If you require all the DNA sources in the world, a scammer will still charm a target into opening it up for them.
...and...
some people are gullible enough to go into a hidden setting on their phone and enable that in order to install an app from a random Chinese website
are kind of contradictory.