Assume we have a password and add a unique salt to prevent various precomputation attacks.

Why don't we do this:

```
SHA256(SHA256(SHA256 ...(Password || Salt)))   

```

So, we have n iterations (like in PBKDF2) and because of the iterations, it should take much longer to compute the hash for a password, which is key stretching.

Can someone explain to a newbie like me why we don't use specific algorithms like scrypt, PBKDF2, or Argon2 and do this?