Of course it does: Not only does secure boot add an extra point of failure, it's a point of failure that's specifically designed to be highly sensitive, and to fail locked, and that hardly anyone in the kernel development community is testing with.
> I'm not sure how this is related
From a computer owner's point of view, the TPM's secure boot functionality exists only to protect against attackers with physical access to the device. After all, if a malicious attacker making a remote attack has the ability to replace your bootloader or reflash your BIOS, they've already got everything.
In other words, secure boot is there to protect against an evil maid [1] removing your hard drive, replacing your bootloader with one that logs your full disk encryption password, then subsequently stealing your laptop and password at the same time. Or something of that ilk.
However, the TPM is insufficient to protect against such attacks.
As such, secure boot fails to provide the one thing it claims to provide.
A serious system - like the xbox's security system - (a) has the functionality on the CPU die, and (b) has the hardware for full speed RAM, bus and disk crypto, all with keys that are inaccessible to the OS.