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?
One reason is the constant stream of FUD from the anti-DRM folks.
https://www.cl.cam.ac.uk/~rja14/tcpa-faq.html
You think all those FIDO members don't care about DRM. That is beyond naive in my opinion. Security is a trust problem, so much should be clear before even starting to discuss it.
Also FUD is employed by presenting advantages of TPM as it often invokes ransomware.
Nice, but probably 99% of ransomware is just executed in user space and starts encrypting typical network drives in typical corporations. Some are more sophisticated, but I haven't seen any bios attacks recently. And why would they? Ransomware is quite profitable.
Yes? Fear, uncertainty and doubt is the correct attitude toward TPMs. (Assuming you count "We know it's going to hurt us, just not how long it will take to happen." as "doubt".)
i have never seen a consumer motherboard with a TPM device in the last 15 years. In fact, the last batch of enthusiast AM4 ones ("pro" model), the TPM doesn't even have the Header populated, only the holes for one that you can solder a header.
And non-workstation office machines from hp and dell ship weird ones that probably won't even pass the win11 test.