There's also the concern of potential sexual assault. If boy and girl troops attend the same summer camps and/or jamborees, what's the likelihood of girls getting raped or sexually assaulted? It probably isn't zero if that happens, especially because there will be leaders there who may have those tendencies not to mention the teenage libidos running around everywhere.
What's the likelihood of women leaders feigning rape or sexual assault to get attention (that doesn't happen though, amirite?!)? Will the increased revenue be enough to cover the extra litigation fees that result from this?
You also have to train new leaders, print more materials, etc with the new packs/troops. Even if this raises enrollment, is it really enough extra revenue to pay for the training, materials, extra weeks of summer camp (or new segregated camps even), extra pamphlets, merit badge cards, patches, etc? Does the benefit outweigh the cost here?
Like I said, you currently have programs that allow boys and girls to cooperate in the same structured environment. Why not revamp those and spend money to promote those? There aren't as many charters for Venturing or Explorers, but that could certainly change.
Age could be a constraint (14+ yrs old) and if this were limited to Cub Scouts, I probably wouldn't have a problem. Once you start getting into the teenage years, things become weirder and harder. If the BSA loses funding because of this, they won't survive. They've already had to raise membership fees multiple times in the past 20 years to keep afloat. Membership has dwindled because of the increasingly progressive policies the BSA has employed (allowing gay members, now allowing transgenders and girls). It's only a matter of time before the organization folds.
It was a very conservative organization for a long time and was very successful. Why change a successful formula?