A bicycle is a complicated object that has many forgettable parts. Everyone knows that there are two wheels (bi-cycle) and that there's a triangle formed from the down tube, top tube, and seat tube. Except, the triangle has a 4th side to hold the steerer and fork (the head tube). Then there are the other details. The handlebars attach to a stem, which attaches to a steerer tube, which goes through the head tube with bearings on each side, and finally tapers at a "rake angle" to actually hold the hub of the front wheel. There is also the rear triangle that consists of the seat stays and chainstays (and the seat tube). You have to put the saddle somewhere, that's attached to a seatpost that goes inside the seat tube and is secured by clamping it in there. With all those in place, the rest is easy -- where the wheels, pedals / bottom bracket, and chain end up are all very natural.

The problem is how often the bicycle is extolled as a simple triangle with some handwaving and two wheels. Turns out all that handwaving is quite complicated. The triangle becomes a shape with 4 edges. There are actually two triangles. And there are complicated details in joining the seat and fork to the bike.

So... I don't think these people are dumb. They have been mislead by "it's just a triangle" when it's actually nothing like a triangle. The devil is in the details.