many people dont want to learn photography. they want to get the photos of their family, their pet. or the nice view of the landscape in front of them.
Or let me rephrase that … sometimes it is much much more important to have the photo in your camera than being able to claim “yeah I did that all in manual mode” … nobody cares about this if you missed the shot.
Personally I have my camera in aperture prio like almost the whole time, as the DOF can have a big influence on the look of an image. i rarely fiddle with iso and shutter speed can have a big impact on the look but those moments are rare for me.