It IS a successful line in at least one way - that Walmart & Target buyers are too uninformed to recognize a good wave from a bad wave, but they know who Spiderman is and mindlessly buy it just like they'd buy a Batman line from Mattel if that deal ever happens.
The problem is that the characters they make are unknown to most big box customers - and if you track comic sales, you know why. The Spoidey waves end up on clearance all the time, so while in the sort term they do get sold into retail, the more they get clearanced, the less likely the big two are to buy the next wave. That's not success.
No problem with them making obscure characters, ever. But they should at least make the classic version. Imagine doing a modern Hypno-Hustler (if that's even a thing).