Thank you Micheal for endorsing that THEORY. In response to Matt, was wondering if I should mention that the beesource guru believed it to be true.
I don't see it that way at all. Excess young bees is just one indication, of many, of the EFFECTS of the instinctive honey bee reproductive process. Reproduction by colony division is a complicated, and care must be given to both halves to insure survival of the parent colony and provide the offspring swarm with the best chance of establishment/survival in a new location. Although quite complex, the bees have had a long time to incorporate those elements of support into their instincts.
Young bees are needed in both halves. Brood rearing is continuous in the parent and the swarm must have immediate replacement bees, during establishment. Brood rearing starts in the relocated swarm with cells barely started - almost no cell sidewall. Urgent. Which brings us to wax makers. The swarm makes no progress without comb. Wax makers are reported to need 10 days in quiet meditation to secrete wax, and the swarm needs a large contingent of those "unemployed" young bees.
Bee crowding is another effect of the process that is considered a "cause." It's automatic that generating two viable colonies in a one-colony space would create some crowding, but it also supports the generation of the wax makers. Wax makers need about 100 degrees F to generate wax. By crowding into the top of the cavity, they can elevate the temperture with collective metabolic heat.
May as well mention another favorite "cause" here on these forums that is an EFFECT. No Room For The Queen To Lay. Reduction of the brood voume by backfilling is quite deliberate and provides benefit to both the parent and offspring swarm. The parent gets a headstart on resupplying winter honey. Note that they only have the second half of the spring flow remaining. It also helps to recognize that their survival traits were developed for the forest where a fall flow is unlikely. Getting the brood nest back to a level appropriate to the fixed cavity size of the tree hollow is also of benefit.
The swarm benefits from backfilling by freeing up the young bees we've been talking about.
Yes, the reproductive process is complicated, but we don't believe any single element of the indications that we see are causes. The bees, or any creature, does not need an excuse for their reproductive process. It is handed down by instinct. We see the whole process as a well-orchestrated scheme that is undeniably effective.