The chief reason that TF Blockees are selling so well and loved by people is that the main TF line has been utter dog shit since at least the tail end of the War For Cybertron trilogy, but who's dog shit kicked into high gear and then some with Legacy being full of literal who's and an influx of AIDs that was frameslop combiners, Unicron trilogy, RID '15, and Gen 2 OC characterd/garrish recolors bullshit. Something Hasbro doubled down with AOP except now we have super literal who's in the form of the 13 Primes and a flood of budget cartoon Optimus Prime/Bumblebees warming shelves while Megatron and Soundwave are overpriced Leader figures and Hasbro having not only learned nothing from the backlash from the Stunticons and doubled down on gouging fans for process of combiner torsos.
Blockees, with their evergreen designs and Action Master nature without the two things that damned that line (costing twice what a regular 1990 GI Joe/Turtle cost and the flood of literal who's new characters no one wanted), make them affordable and more appealing to TF fans who despise the direction the main Has ri line has gone into.