I think it’s more a consequence of what its peers do than of Williams itself trying to lower their admissions rate. Many of Williams’s direct peers, like Amherst, Pomona, Swarthmore, as well as several Ivies, like Columbia, Dartmouth, and U’Penn also got rid of the SAT subject test requirement after asking for them for many years. I’m not sure who led the charge (apparently Columbia according to the article below?), but Williams just followed the common trend. And their admissions office does mention that from their experience the tests provide little of note for the consideration process. I think these colleges know what they’re doing.