For one thing, I hate the idea that such vulnerabilities can be used against me (e.g. to exfiltrate my data), but they cannot be used in any way to help me, such as allowing me to sideload a third-party ROM (such as LineageOS) and continue to use the phone I paid $1000 for after the OEM decides they don't feel like supporting it anymore.
Because (a) it would let you root your device, allowing you to do what you want with it (b) it would make these 400 vulnerabilities especially dangerous
Best to use a bank which treats you like an adult and trusts you to make grown-up decisions about using a rooted device. Monzo fits into this category.