This is a fairly vacuous remark, if I'm frank.

The problem isn't that you have to learn another framework (although it does become a problem when they're all slightly similar and they start to meld together after the umphteenth, not to mention that learning slows down with age). The problem is that each frameworks brings along new edge cases, new problems and forces you to reinvent tools you already had for this new framework. Although learning new shit can be exiting, at some point, you gotta stick to something for a while so you can also actually build a lasting product with it, rather than building a new prototype but never finishing anything because you're distracted by a new shiny.