There's more to fork design than just tire and fender clearance at the top of the fork. You see, when you want to run really wide tires and fenders, you don't want your wheel to hit your foot when you turn (toe overlap). Several other factors need to be considered and designed into the fork to move the wheel and fender forward and still allow for desired handling (steering) for the bicycle. But the designs available all had some big flaws.
Now, you can either accept that last sentence, or if you are like me, you want to read more and understand those big flaws. Warning: it's a long article.
We developed the Phinney Ridge light weight disc fork to be attractive, very light weight, and specifically designed for the evolving trend of really wide tires and fenders. The Phinney Ridge fork allows us to build your bike for tires from 28mm wide all the way up to 54mm (or 2.125 inches) wide and still have plenty of room for fenders. All of this with better handling characteristics, and most importanly, no toe overlap.
Why not carbon? A lot of people think they want a carbon fork, and we have nothing against putting a carbon fork in a bicycle. We use carbon forks all the time. But, we decided that our Phinney Ridge fork should be a 'forever fork' and carbon forks are not that. This fork is as light as many of the carbon fork options available in this category, looks great, and will provide the customer with a lifetime of service.
If you're interested in fork design for wide tires and fenders, I have a more technical article here: Trail Mix for Wide Tires