The reason this matters is mechanical. Stolen passwords from one site get tried automatically against thousands of others. If your email password is the same as your old shopping site password, and that shopping site was breached three years ago, your email is already at risk.
Memorizing 80 unique passwords is not realistic. The fix is to stop trying. A password manager (1Password and Bitwarden are two good ones) generates and stores a unique password for every account. You remember one strong passphrase to unlock the manager. That is the whole system.