Maybe they were having a hard time meeting their recruiting goals, and needed more bodies for their growing scale of operations.
Or maybe with their increased scale, they have recruited enough talent to make inroads into the female market for recruits - which could be a big development as muhammad never cracked that code himself.
It may be more related to the lack of enthusiasm for breeding among younger people today; the US is doing the same thing, trying to shoe-horn females into combat roles for which they obviously are not designed biologically. I know the San Bernadino female had recently had a child, but it is safe to assume that midnight feedings and dirty diapers didn’t agree with her. She found an easy way out (in her mind); I think a lot of our female recruits are doing the same (moving from their parents’ home to another “parent” - the military).