Our association saw this, too. As it turned out for us there was a causal relationship, but not as you describe. Several years ago there were a few hockey guys, blessed with having only daughters, that happened to have girls about the same age. They fought for and received segregated ice for 8U girls, good for them [no sarcasm]. They dressed them all up in pink, convinced a bunch of their friends to join, had bowling, pizza, and movie parties together, skated with the gophers - fun was had by all, and the look of a giant bottle of Pepto Bismol being spilled onto the ice was cute. That group of girls has moved on to 10U, so many of them that after dragging up 4 or 5 siblings, coaches kids, and board members kids from the 8U, they were able to field 2 10U teams - awesome.Number of girls playing 8 years ago, 5 years ago and today. It's grown significantly since we split the boys and girls at the mite level.
However, gone from the 8U are those kids, their parent coaches, and, as it turns out, most importantly, the parental recruiters. The association is left to figure out what to do with an 8U group that has about 1/3 the numbers it had 2 years ago. The ‘research’ did not show in this case that an 8U program caused more girls to play, but rather more girls had caused an 8U program. I’ve heard from folks at a couple other associations that have experienced the same thing: 8U numbers peaked then dropped (those parents started something that the association had not bought into and perpetuated). In addition, those coaches (usually a couple dads of the 5 and 6 year old girls) now realize that the sleepovers were a good time, but the girls didn’t learn much about hockey.
More to the subject, those 8U programs are left with 2 or 3 girls that chased the older girls and can skate, the remainder of the 8U are either just getting started, or were more interested with the face painting parties than with hockey. What do you do with the 2 or 3? They want to go, go, go, but the few coaches that remain at 8U need to spend their time and energy at the level of the majority of kids. Do you tell them to skate with the boys, or tell them to go play basketball this year, and maybe their peers will have caught up with them by next winter?
Even at the 10U level, if the association offers one B team, and 1 or 2 girls are well above the rest, how is the program served by stunting the development of those 2 girls? How are the other girls on the team affected by having 1 or 2 kids that can handle the puck and skate, which in outstate 10UB hockey means they can go end-to-end without much resistance? Is the association better served by forcing those girls to 10U rather than squirts, is the high school program eventually better served, and most importantly, are the girls better served?