With an HDD, your operating system can (mostly) directly access bits on the magnetic disks, so you can wipe them by just writing 0 to it over and over (historically, there was a paper saying 7 times would make any bits unrecoverable - this changed as density got higher)

With SSDs, your operating system has very little control over what bits a write is touching, a lot more was moved into the firmware on the flash memory itself

So SSDs need a special command “Secure Erase” to wipe them