Originally, they promised TPM 2.0 could be added via a card or chip nvme I guess. Then it was motherboard manufacturer specific add on cards. (Like this article talks about https://www.tomshardware.com/news/where-to-buy-tpm-2.0-for-w...)

More recently they just decided you need a new machine entirely (to drive revenue to their oem hardware partners).

One handy thing is - just turn off TPM 2.0 on your modern machines bios and you can keep running windows 10.