I feel like you're getting a bit silly here on two points.
First off, I don't think a two or four-year-old looking at a D&D book "generates future players" in any meaningful way. Otherwise I'd have been a zoologist, paleontologist, or pilot or something. And indeed pretty much everyone looks at tons of cool-looking books which have zero impact on their future life choices at that age. Definitely the most influential period for artwork on my hobbies and interests in later life was significantly later than that, at eight plus. I'm sure that varies, but I very much doubt it's normal to get into a hobby because you were exposed to it aged two. Otherwise model railways would still be big.
Second off, I think the idea of two or four-year-olds "getting a kick out of" D&D books is er, questionable. D&D often features some pretty terrifying and/or violent imagery. I know that, as a kid, even a fair bit older than that, the imagery from some stuff that seems utterly innocuous as an an adult, genuinely gave me nightmares, and I was not a "sensitive" kid - quite the opposite. The Monster Manual in particular I would question giving to a kid under about seven or eight. Some kids will be immune, but some kids watch Alien aged eight and don't blink an eyelid, so that doesn't mean much. I don't think WotC are, nor should be targeting "two to four-year-olds" in their main book line.
Sorry, no.
This is not a reasonable approach. It's a facile one that doesn't hold up to scrutiny. WotC certainly attempt to find out about the market, but how successful they are, what their methods are, and how much they actually know is massively open to question. It's easy to be snooty and dismissive towards people who are suggesting WotC are perhaps making a mistake, to take a high-handed and contemptuous position of "Oh look, an internet-man thinks he knows what might work! How tremendously funny!", which is basically what you're doing, even if you don't mean to.
But this is WotC. They are deeply fallible. This is the company that came out with 4E, and more importantly, 4E's market strategy and product approach. You think they did less market research then? You think they were less competent then? You think companies continually get better at this? (hint: they do not) You think the same company that had flops with so much 3E and 4E material is always making good choices? You can't run with "Companies always know better!" whilst there's clear evidence of said companies making serious mistakes. 5E exists because WotC messed up with 4E.
5E's success seems to me to be very simple - they're essentially starving the market rather than flooding it, thus absolutely anything they release at all is almost certain to sell well. It's a good strategy for high profit with low financial investment, there's no denying that. But that doesn't mean it's actually what would be most profitable or most successful for D&D overall, and there's little to no evidence WotC is even considering other strategies. All the evidence we have, I would suggest, is that WotC, very early in 5E, before release even, decided on an extremely conservative sales strategy for 5E, sticking to a small number of products which were sure things, and the odd opportunistic media tie-in (nothing wrong with that!), rather than going for a more maximal strategy. I mean, do you not see how cautious they were even with Eberron? I don't think they really want to sell new versions of extant settings. I'm less sure, though, that that's because they won't sell - I suspect it's more out of a wild abundance of caution and an utter, stark terror of flooding the market.
