the looks of the wallet can also be different, even the logo. a user that downloads such malicious wallets doesn't pay attention to those differences either, even if they do it would look like the new version's new looks.
It is also trivially easy to create a clone the looks like another wallet. That's probably the easiest step in the entire process of creating a scam wallet. To program a wallet to steal seeds, keys, or coins, you at least have to know a bit of programming. Literally anyone can mimic fonts, colors, and layout. Being closed source doesn't help this at all, since the underlying code isn't the part a scammer needs to copy.
Exactly, having the source code open doesn't guarantee that the files you download from app stores are the same. And even if they are, it's not guaranteed that the source code was inspected by someone who knows what to look for.
Which brings me back to my original point. I'm sure you will always have plenty of users, and people who blindly download apps from the app store don't care about the code being open source. But serious bitcoin users are going to be downloading open source wallets they can verify themselves direct from GitHub or the developer's site, and not from some scam filled Google or Apple store.