Frankly it takes quite a lot of skill to use a manual properly, which is why we enthusiasts enjoy it, and most people simply do not have the inclination to completely master the intricacies of one. How many people actually 'heel n toe', block change, rev match or are even in the right gear at the right time for the speed and road conditions they face? Many people just judder along at too low revs, drag the clutch on downchanges, often start in 2nd, and are just cruel and harsh with the clutch work.
The reason that most people fail to use a gear box properly is because the "approved" driving instructors are not allowed to teach them how to do so.
Today they are taught to get into the highest gear possible as soon as possible as it is more economical, they are taught to slow down using the brakes, not the engine and so on.
When my kids were learning I went out with the instructor and after one lesson questioned this. He agreed it was rubbish but it is what VOSA require. Driving the way I was taught would result in a "FAIL".
After they passed, both first time, we paid for a "Pass Plus" course. The instructor then re-taught them how to use an engine and gearbox.
I think the issue is that 95% of drivers are not driving for enjoyment: they drive to get from A to B and an auto box makes life easier.
Another issue that pushes people to auto boxes is that some gearboxes are (still) not easy to use and ill matched to the engine & clutch.
When the makers get it right changing gear is a delight. When they don't it is a chore.
