So How did they get to 55%. Are they just refusing to admit more than a certain number of men? Or is the a more organic shift through staffing and support changes?
The acceptance rate for males is 9%. For females it is 21%.
Fundamentally, most sensible people do not want to create additional hassles in their lives by choosing to become a minority. If life in Bangladesh had been as great as life in the U.S.A., my parents certainly wouldn't have moved to a place where they looked different from everyone around them. When women consider going into male-dominated fields, that's essentially what they're signing up for. That dissuades a lot of candidates who would otherwise be promising.[2]
[1] While men and women perform similarly on average on both tests, there are significantly more men who score in the top 1% on each test (for whatever reason). In the numbers-driven world of law school or med school admissions, that factor is outweighed by the fact that women tend to have better GPAs and as a result have similar admissions composite scores.
[2] The same is of course true for men considering women-dominated fields. There are many men who would be phenomenal teachers, nurses, child-care workers, which are solid jobs with good pay, who very reasonably do not want to put up with the hassles and skepticism that would come with being a man in a women-dominated field.