It also seems to come from complaints that the results SKR described don't meet with our biases. So they must've done it poorly because I disagree with the outcome. It's quesitonable logic.
Perhaps. I'm not going to assert that is going on for any particular person, but it is common.
As far as omitting the over 35 crowd, I would think most people would be aware just how common youth marketing is. WotC wanted to be the overall market leader for the TTRPG segment, so they basically had to do this.
Also, we can remember they already had major games that were likely most popular with folks under 35. Getting information so you can determine how the different properties might align would seem important.
WotC doesn't care as much about the over 35 crowd because they're a small fraction of the marketplace, as a whole they spend less, and it's difficult to expand the market for people this age. You might not like it, but that's just reality.
We should note that this stuff was done 20 years ago, and does not speak to WotC's current cares. As of the demographics they released a year ago, the D&D community was...
Age 15-24 ~ 36%
Age 25-34 ~ 36%
Age 35+ ~ 27%
We can say that 35+ is not the majority, but 27% of the market is a large fraction, not a small one. The repeated nods to older settings seems in line with this - they aren't entirely focused on older gamers, but they are doing some things relevant to them.