If you look at IBM's TPM 2.0 implementation[1], you can see that they don't use any well tested libraries for crypto primitives, but rather uses what looks like home-cooked crypto implementation.
Microsoft, on the other hand, seems to support OpenSSL and wolfSSL in their simulator[2].
Sure, but what exactly do you think real TPM manufacturers are putting inside them? They must run some crypto code, do you think they won’t just reuse IBMs emulator? Or that they will come up with something more secure?
IBM's implementation is really scary. I read through the codebase and my WTF meter went through the roof. It looks like the codebase of some evil genius that invented a world of coding practices of his own.
tpm2-tss is not an implementation of a TPM, it's a client of the TPM protocol that talks to a server. The server in this protocol can be a real TPM reached by a linux device file or a TPM arbitrator (in kernel on in userspace) or a TPM emulator (the IBM one linked above), etc.
tpm2-tools are CLI utilities that use the tpm2-tss library.