In LXF162, Mayank Sharma's article, the penultimate Q-A says "there is no standard way of disabling SecureBoot" but Microsoft has "allowed OEMs to implement customised mechanisms for disabling the feature" (jolly decent of them, although not in ARM machines).
So if someone wants to install Linux on the Windows PC they bought from Currys etc (like most of us start), they must first clear the hurdle of finding out how to do it. Enough to put many off curiously trying a live Linux CD - something MS hate people doing because they might like it.
But disabling it might not even be possible. The PC builder is allowed but not required to offer a way to disable it and I suspect that most will not bother to do so. Even if it is possible to disable SecureBoot they will probably not bother to document it. The days of getting decent documentation with PCs (or any gadget) these days have long gone, other than shedloads of safety warnings and green hectoring. As long as Windows runs, the PC maker will regard it as job done. The only exceptions will be PCs made to order, such as for server farms, and home-built.
Then in the final Q-A he says "no one is arguing against the SecureBoot mecahnism". Wrong. I am, and looking at internet debates I am not alone (despite my sig, LoL), because I realise that it can and will be abused by a monopolist like MS. In a nutshell, this is part of an ongoing effort to turn PCs into appliances anchored to shopping, social media and paid entertainment - through narrow and controlled channels.