Brute-forcing private keys and encrypted wallet are 2 different thing,
1. Brute-forcing encrypted wallet is faster if it's encrypted with weak password.
2. Brute-forcing private keys is only possible if it's generated with weak RNG or implementation, which significantly reduce search space.
This is like digging for gold and by technology going up i believe oneday it will be possible to brute force about 20-100 wallets each year using some crazy asic machine and a whole industry will be built around just this idea.
It's called theft.