A surgeon still spent many years studying medicine at a broad level before moving into training for that specialty, though.

And many developers I know do end up specializing in particular sub-fields (ML, databases, whatever), but they already have a wide breadth of knowledge and experience to serve as a foundation underneath that. In contrast, I also know some developers who didn't take that route, and jumped into specialization early, and who are completely useless at productionizing their work.