Essentially new moulds, and a production run that is likely to be a tenth of the retail Generations toys, with limited redeco potential (particularly at these prices), is the reason for the higher prices.
Would people have bought these if they weren't accurate to the originals with their modes and sculpting... I think they needed to go the extra mile with making them pretty much from scratch, and charging a lot more for them, as they may not have been able to slot them into the current Generations series.