Westgate skates in such an unmistakable way that he'll be talked about for years as being one of the best. If you look at the list, his name most definitely fits on there. To over-dramatise things, SOTY shouldn't just mean 'who had the gnarliest footage this year?' (which is kinda like asking 'which guitar player played the fastest solo?'), more, 'who merits a place in the history books?'.
It's all subjective though and you could totally make the same argument for anyone on that list. For me, Westgate sits alongside Carroll, Rowley, Grant etc in having his own very distinct thing going on that I don't get so much from the others.
Whatever. Phelps' stupid whims decide it anyway so none of this matters.