Why? The booming boardgame hobby is fueled by the 25 to 40 year old crowd, people who have no problem dropping $300 or more annually on a hobby. Hipsters, educated couples, urban singles, young professionals with kids. The RPG industry would kill to have those 'problematic' demographics. WotC's devs have explicitly cited the boardgame boom and questioned why D&D hasn't been able to see the same growth. I'm sure they know (since they have some very successful boardgames themselves) that the enormous growth in hobby boardgaming in the last decade has not been fueled by 12-20 year olds.
And if the D&D market really is 70% 25 and under, why all the references in the 5E books to Keep in the Borderlands, the 1E PHB, the Giant series, etc? Whey the skinning of the 4E beginner's set to look like Mentzner Basic? Why, after the polling of 100,000+ playtesters, did WotC keep hoary old tropes from TSR D&D?