If there is a direct female equivilant then often the all women orgamization may feel that it they are taking potentials away from them. I know that Girl Guides of Canada had a fit when Scouts went co-ed because parents who have both boys and girls were more likely to pull their girls out of Brownies/Guides and put them in Cubs/Scouts. However, both organizations still remain quite active, at least in this part of Canada
As a (former) Girl Guide (in brackets because once you're "enrolled" (initated) and receive your Guide pin, you'll always be a Guide and can return to the movement any time you want) I'm also really glad that Guides chose to remain all girls!!!