If your wallet is unmaintained, you have other problems beyond (extremely rare) root CA revocations.

As far as I know the only time a CA in wide usage has been revoked entirely is DigiNotar.

One advantage of doing it this way is if, for example, a widely used piece of community infrastructure (e.g. bitcointalk, reddit, whatever) decides to become a CA, the Bitcoin community can decide to have different inclusion rules vs the OS/browser root CA programs. For example we'd probably relax the constraint to use an HSM and just ensure that the rendering of the asserted identity isn't confusible with other kinds of more strongly protected identities. For example no forum usernames like "foo.com" but rendering it in the UI as "Reddit forum user foo.com" would be OK.

Also you don't get problems due to old operating systems not including new certs.

Finally, Linux doesn't have any kind of standardised cert/keystore API. There are a few places where popular distros put certs but AFAIK they aren't standardised and there's no standard code to load them. So that's another reason why there's a built in store.

But yes, this is a debatable topic on which reasonable people can disagree. The API makes it easy to use the platform OS store for wallet devs that want to do that, and I think using the platform store on Android is the default. It's only on the desktop where we fall back to a different store.