Being able to learn things quickly is an amazing skill to have—even more so for developers because of speed of technology.
Most people change careers 15 times throughout their life. Not jobs, careers! So it’s safe to assume that the average developer will have multiple jobs throughout their career. Each job change has the potential to require different skills.
The things that were commonplace even 15 years ago for developers are now obsolete. So, yes, it’s important for developers to be able to learn while on the job. I would argue, however, that a more important skill is being able to choose what to learn next.