If Fantastic Four toys don't regularly sell than they aren't put out because they can't justify the cost of making them. Putting out a new product rather than a failing one is far less of a gamble. As a company would you really sell something that you aren't making enough on to justify continuing to make them? We put up with this all the time in comics so I hardly see the problem in toys.
Lets not forget that Spider-man was in the FF position before recently and Marvel and whatever companies they had been affiliated with had no problem putting them out. They didn't care because they could move Spider-man merchandise without much hassle, that is not the case with the FF.
But here's the thing, Marvel still does make Fantastic Four merchandise, just not much of it. They have T-shirts, prints, trades, coffee mugs, costumes, minimates, keychains, etc. And to be clear that I could pull right off their Amazon page. Even on their website you can get FF material. Can you find it in stores, not usually but it is online and from them. Doctor Doom seems to have been getting the most attention as of late (various statues and an Avengers titan hero toy for instance) but as I've clearly stated, companies will move what they can sell and the FF themselves don't do that as well as they could.
Also when did I blame the movie for them not selling? The movie certainly didn't help Marvel in the slightest but I don't blame that for the lack of interest in the FF themselves.