I agree with you about looking at who benefits, and how they benefit. And about there being an epicenter somewhere.
While the most obvious (to most) conclusion is that a pedophile took the girls for his own twisted reasons, there are other possibilities that deserve consideration. IMO
IMOO...Whoever did this wanted it to be known the girls were taken and wanted the girls to be found, and clearly had a message to send!
If the bikes/purse were staged, as some believe, I don't know why the perp would go through the trouble or take the risk of being caught when they already had the girls and could have just taken the bikes with them or disposed of them in a random and more remote location. If the bikes weren't staged and just left at the lake in a random abduction, I don't know why the "identifiable" bodies/evidence ended up so close to home, when the perps had 5 months to dispose of them in any location and manner that would prevent them from being found or identified!
RSO/pervert/*advertiser censored* ring doesn't fit into my scenario because there would be other victims or similar crimes in the area before and after this and there would be more info and warnings released by LE to protect other children.
Timing and location from day 1 tells me this is "home grown" and related to family affiliation/lifestyle (not done by family members directly)! This family had affiliation with some very scary, intimidating, threatening people with rap sheets a mile long, who in my opinion, would not think twice about killing someone for any number of reasons!
And yes...I have specific people in mind with media articles and a (disturbing) youtube rap video...but I might be restricted by "rules" since they haven't been classified as a POI or "suspect".