TPM vs Full-Disk encryption + BIOS/boot password

So I've been looking into the Win11/ TPM kerfuffle a bit, and I'm trying to understand exactly what the point of TPM really is over simply having a BIOS/power-on password with full-disk encryption, and just....remembering a decent set of long passphrases?

If the BIOS and startup are password-locked, then a potential adversary can't use a USB etc to tamper with the bootloader and lift the key next time you boot. So they basically have no choice but to remove the …

bios boot disk encryption encryption password privacy tpm vs