/facepalm
TPM can't rootkit anything. It doesn't have interrupts, and it can't write to system memory. It's not much different from any device you'd connect over a serial port, meaning all your computer can do is send and receive data from it. Components attached to your PCI-e bus will have a much greater ability to rootkit you, like your GPU, your ethernet adapter, or even your USB devices. Yet, despite your yammering, you don't think twice about any of those.
Its only purpose is to serve as a witness, nothing more, nothing less. Where I work, we use these a lot for systems that have nothing at all to do with Microsoft. No windows, no azure. Only linux. Why? Because it provides additional security assurances, which any end user can benefit from, or even add their own assurances. Another analogy is that it's more like a yubikey that your computer also sends boot information to. It's also an open standard. Anybody can make a TPM. The documentation for the entire spec is publicly available, free of charge.
You should really learn more about things before running your mouth about them. You may as well argue that all encryption is designed so that Microsoft can rootkit you, and it would make just as much (non)sense.