It mainly boils down to the TPM requirement. TPM 2 offers much better security and unfortunately TPM 1.2 and 2 are not compatible due in part to the types of data they can store. There are a number of features both Azure centric and specific to Windows that do not work on older TPMs and that again is due to the data that needs to be stored and the cryptographic algorithms that are used. An example is that TPM 1.2 only supports SHA-1 for hashing which has been considered weak and not recommended.