A wallet dev absolutely *can* write a custom wallet that implements the same policy using tapleaves. But then he loses the interoperability that is a huge selling point of Miniscript. Custom tapleaf wallets cannot easily be exported and imported into hardware wallets and Bitcoin Core. Miniscript wallets can be. Plus, for some policies, using tapleaves is less efficient than using OP_IF: https://x.com/salvatoshi/status/1989270625454584132
Consider changing the BIP instead of demanding that innocent users change their wallets in ways they may not know how to do and which would often make them worse.
