That was to let girls in.
I guess that's true. 2016 Marine Times article:
"After years of debate about whether to require women to do pullups as part of the PFT, the flexed-arm hang era is officially coming to a close. Starting next year, all Marines, poolees and officer candidates will have two choices when it comes to flexing their upper-body might: pullups or pushups.
Brian McGuire, deputy of fitness branch for TECOM's standards division, called the flexed-arm hang an "inadequate test of upper body strength," adding that the pullup is preferred because it requires an individual to overcome his entire body weight, while a pushup requires he overcome only 70 to 80 percent. So why include pushups at all?
McGuire said it was because the Marine Corps didn't "want to create a manpower problem by having some female Marines failing."