Obviously I don't have any hard evidence so I can only go by my own observation. I believe that the reason why we have so many Bumblebees from Hasbro is because the stores demands them. Possibly due to the incredible sales that the 2007 deluxe Bumblebee had and the huge demand afterwards that they have gotten stock with the notion that Bumblebee is what Transformers is all about. Hasbro basically exploits this by promising Bumblebees everywhere hence why there are so many Bumblebees for each case.
I think that Retailers wanted more movie stuff because they think it's popular and toy wise, they identify movie with Bumblebees and Primes hence all the releases and repaints.
Personally speaking, I don't think they are over Bumblebees and Primes despite the issues with the shelf warming toys from DOTM line. The reason why some waves were cancelled may be simply because the stores were still overwhelmed with the peg/shelf warmers so were reluctant to buy more. However I doubt that they would have learned their lesson and once stock cleared, they would end up demanding the same crap over and over hence the movie trilogy line.
There were some toy types that were release for the different movie lines that remained shelf warmers for months even years but despite this, the stores kept buying the same junk for every movie. To me, this shows that the retailer guy buying the stock from Hasbro is not really well informed of what works and what doesn't.