Manuals are tiring for long trips. In the US, many individual states are larger than the UK, and it becomes a literal pain to have to constantly shift gears because of changes in traffic. Also, in the US you very rarely have to worry about some idiot rolling back and hitting you when trying to go at a stoplight because their foot slipped on the pedal. Low speed control is so much easier on an automatic (take your foot off the brake, it moves forward slowly- great for really poor traffic) and backing up is much safer (for the same reason, you don't need to apply any gas to move). You can even control when your car switches gears by letting up on the accelerator slightly to increase, and braking to decrease. It is a good skill to know, to drive a manual, in case it is ever needed, but honestly there is very little true advantage to a manual that you can tangibly feel on an everyday basis. No design of anything is ever made safer by having additional moving parts, or more integral human input.