Part of the reason why people can learn to drive in hours is because they have been riding in cars as passengers since birth. Though new at driving, they have lots of contextual knowledge and awareness. If you took someone who grew up on a desert island and taught them to parallel park, it would take considerably longer.

Likewise, experienced web developers have years of contextual knowledge of CLIs, documentation and coding. An experienced dev can reasonably be expected to bootstrap a JavaScript app within a few hours, even if they only used jQuery in the past.