Regular users don't actually know anything about the difference. They look at how many megapixels the camera has and the resolution of the screen and things like that, because they're numbers you can compare. Regular users don't know what "stock Android"
is. And then they come home with a phone full of bloatware and complain about it after.
Nobody actually buys the phone for the bloatware. These companies are wasting their money developing it. They just want the phone with the better camera.
The real problem is that techies can't improve Android because the hardware vendors are shipping custom kernels and their hardware can't use the stock kernel. So Android is "open source" but there is no ecosystem of people scratching that itch with the improvements flowing to the ordinary users because it's so hard to modify what came with your device. Especially when many of the techies still care about the better screen and camera.
Think about it this way. There is no reason every Android phone on the market shouldn't come with the option of stock Android. Even if you think the majority of "regular users" wouldn't want it, the availability of it would get them a few sales from techies, right? And then we would really find out what people want, because they get the choice without it being tied to the rest of the hardware.