Many of the apps that people need to have smartphone to access will not run in an Android sandbox. Banking apps are the obvious example.
Not to mention that the options outside iOS and Android are slim and for the most part bad (or atleast simply even worse than those).
Is it because the sandbox is bad and does not perfectly simulate the computing environment of a real device?
Because to me it sounds like a cat and mouse game that Google and banking apps are destined to lose.
It's because of the Play Integrity API, which AFAIK runs downloaded binaries in the DroidGuard environment: https://en.wikipedia.org/wiki/Play_Integrity_API
The strongest levels require hardware key attestation (which, in my understanding, uses a certificate that's baked in secure hardware and signed by Google): - https://grapheneos.org/articles/attestation-compatibility-gu... - https://developer.android.com/privacy-and-security/security-...
There is hardware attestation that prevents a perfect sandbox from being possible.
Unless you know how to build a sandbox that can simulate a TPM with a key inside that only Google knows. Or something like that. I'm not an expert but there's plenty of information on the internet about this. It's definitely more than "the sandbox is buggy".