What's wrong with using plain SHA-256 to hash passwords?

SHA-256 is a fast, general-purpose hash designed for data integrity (checksums), not for password storage. Its speed is a liability here — modern GPUs can compute billions of SHA-256 hashes per second, making brute-force and dictionary attacks against leaked hashes fast and cheap. Purpose-built password hashes like BCrypt/Argon2 are deliberately slow and often memory-hard, making large-scale cracking far more expensive.