That's because "3" addresses are all P2SH addresses which are the RIPEMD160 hashes of a script. The addresses that haven't encoded a segwit script that is. Bitcrack's using a bloom filter that can quickly check if a hash of a private key matches a bunch of RIPEMD160 hashes of the input addresses (that's why it's more efficient to put many addresses in the input file at once).

A script is not generated from random bytes like a private key (according to this pictograph), but it's just a redeem script anyway if we somehow were to obtain the public script for such addresses, or guess what kinda math problem someone would make into a redeem script, then only the solution to that problem  (which is sometimes very easy) has to be brute-forced to spend the input, and bitcrack is completely incapable of doing because it works in terms of private keys.

But it should be possible to brute-force bc1 addresses since those also use private keys, if that's not implemented that'll make yet another good science fair project or even a Google Summer of Code project