Great in theory but difficult in practice. Developers rarely ever have the luxury to pick up a book as a means of getting up to speed when there exists online resources like Google and StackOverflow where you can easily find posts that answer your query string(s) verbatim.
If you don't know enough to ask high quality questions, SO and Google won't help you.
If you're lucky, G will lead you to tuts and repos with useful code.
If you're not, you'll make a ton of stupid beginner mistake and be overdrawn on the technical debt account before you even start.
In other words, the thing that makes software so unique and valuable, is the very thing that most organizations don't take advantage of. They think that if you throw it away, you are scrapping something akin to physical materials.
Shame, really.
That's something I've seen getting much worse over the past decade with the proliferation of frameworks. What you call "getting up to speed" is tempting to call "playing with". People work with tools that they have no knowledge of. Learning on the job is good, but I think one should have at least an idea of how the tools are supposed to be used and how they are implemented before doing anything else than throwaways.
I don't know how to fix it really, it more of a cultural thing than a technical. Knowledge must somehow be cool and respected again. Or maybe I'm just getting old and this is really a faster way of building things. I just can't think of any other area where professionals jump to the next tool without even learning the one they use.