[waych]

TPM is typically implemented in firmware for consumer boards. Having the option to upgrade to a hardware TPM module is nice, but probably not necessary for the vast majority of users. Hardware TPMs also come with their own sustainability questions regarding bugs/upgrades and how/if that process works. This is hard to do without compromising the benefits of using a physically separate TPM unless the end-user takes some form of responsibility in the custodianship themselves (which is not likely at the consumer level).

Considering that the vast majority of boards aren't going to need the header, the board manufacturers can scale cost reduced versions for the masses and spin versions with a couple more headers for a couple more dollars for the fringe users that want them (pre-)populated. Seems like a rational business decision?