1. You can only execute binaries together if they're signed by the same key. 2. Each person has to have a unique signing key. 3. If a user wants to execute a pre-existing software, and something compiled by themselves, both need to be signed by the same key. 4. This means you need to re-package and sign every single program you'd ever want to use together with your own code again, in new packages, and submit it all to Google Play.
This means every Termux user that would want to ever run gcc would have to
(a) submit every single hello world they write to the play store to try it. And every single run requires a full app update, and (b) additionally repackage and submit all linux packages, signed with their own key, to the Play Store.
This means to even compile and run Hello World, you need to submit several hundredthousand packages to the Play Store, wait for approval, and download them all.
Yet at the same time, Google Chrome can use WebAPK and auto-generate APKs on the fly with custom code and install them on the device without going through the Play Store.
The alternative of course is not being able to use a phone as general purpose computing device, but considering Google advertised Android as exactly that, that's getting close to fraud on Google's part, removing functionality after a sale.