Exchanges and wallets are two different things.

I don't know the exact criteria required to list an app on playstore or app store but it will be according to the nature of the utility and when an app involves fiat deposits then KYC must be mandatory for the regulations' sake which doesn't eliminate the scammers completely but narrowed them down from ocean of them.

There are also some applications are known scams still exist on the app stores.

For example Freewallet is a known scam wallet but it's still available on both playstore^[1] and app store^[2].

1. https://play.google.com/store/apps/details?id=app.frwt.wallet&pli=1
2. https://apps.apple.com/us/app/fw-secure-defi-crypto-wallet/id6470998165

So as user you also need to have little responsibility while choosing a wallet for your crypto assets.