I spend a fair amount of time offering electronics/firmware assistance online on various forums. You'd be amazed at how many people have problems just doing this. Seeing a circuit, collecting the parts from a variety of sources, and putting it together is trivial for those of us who have been doing it since we were teenagers. For those completely new to electronics, there are many little hurdles among the way that can eventually cause them to just give up.

Yes, these guys are monetizing a simple concept, but they are providing value. Value is worth paying for.