Secure boot and TPM are tools for (among other things) making sure nobody (E.G. a virus or worm) has tampered with your OS and bootloader. You can for instance use both on Linux, it's just by default they come preloaded with Microsofts configuration for loading Windows, and the technical knowledge for how to reconfigure it is a bit arcane.

It's an excellent security tool, it's just abused by Microsoft to discourage competition.