I could try and weasel out, and I kinda will, because that's a bit stronger than I think my argument really is, which is that if something is popular, it is likely to be better. (Well, that's not the entirety of my argument, I'll come back to that for a second.)
When you assert the strong form, like you just did, the argument becomes exceedingly silly, because rephrasing almost ANYTHING short of mathematical formulas or laws of physics as a Universal Truth makes it at least somewhat silly. But when you look at it as a probability rather than as an absolute, yes, you should expect more popular things to be better than less popular things, no? Not necessarily even overwhelmingly so, but more often than not, right? And quite often, when you scratch an argument for why something that has lost (rather than some new innovation) is better than the thing that became popular, often what you find underneath is a mismatch between what the arguer thinks is better and what the people who chose the popular thing think is better. And maybe they're wrong about what's better, or maybe they were right about what was better given certain constraints that Moore's Law or the cloud or whatever has made irrelevant and now they're persisting due to network effects or whatever.
But to go back to the original poster, who's a Perl programmer trying to figure out what to do with himself. I think writing off the popularity of languages that followed Perl as being due to fadishness, rather than actually investigating why people chose to develop new languages, learn them and build tools for them, is putting an obstacle between yourself and learning new things. You may learn that people had bad reasons, or that they had good reasons at the time but you can do something better than what they had to choose from then. But you'll learn new things, rather than closing yourself off to them by writing off new things that replace what you know best as "fads" and people who adopt them as driven by something other than merits.
It's sort of the liberal flip-side of Chesterton's fence -- Chesterton says that you shouldn't tear down a fence until you can understand why it was built, i.e. you shouldn't change something unless you understand it. The converse is that if everyone keeps tearing down a fence, you should understand why before you put the fence back up again.