I just looked it up again to be sure, and I am slightly mistaken. OED has both forms in use in the 1800s and early 1900s, but all usage examples from the second

I just looked it up again to be sure, and I am slightly mistaken. OED has both forms in use in the 1800s and early 1900s, but all usage examples from the second half of the 1900s onward is -ize only.