It's just one of many reasons why Microsoft alone shouldn't decide what operating systems can work on UEFI machines. If the future is UEFI, then we need an industry body like the W3C or something to work with OS vendors, not just Microsoft.
There are plenty examples of companies keeping something secure. There aren't many of industry bodies.
I'd trust a bank (well, some banks) before I'd trust either the W3C or IETF with the keys to the universe.
An alternative was producing some sort of overall Linux key. It turns out that this is also difficult, since it would mean finding an entity who was willing to take responsibility for managing signing or key distribution. That means having the ability to keep the root key absolutely secure and perform adequate validation of people asking for signing. That's expensive. Like millions of dollars expensive. It would also take a lot of time to set up, and that's not really time we had. And, finally, nobody was jumping at the opportunity to volunteer. So no generic Linux key.