I could learn and use $latest_thing, and maybe it would be great. That will triple the time taken to develop, but whatever. However in a couple of years time when I come to need to write something else, $latest_thing will be old hat, and replaced by $shiny_and_new. Rather than having 10 years of nice simple code based on jquery, I get some based on Angular, some on React, some on Vue, some on Meteor, or whatever.
I'm not a programmer, I'm not a wireman, and I'm not a carpenter. I program in the same way I'll run a network cable or get a screwdriver out, it's a tool I can use to solve a specific task. I like tools that are the same, year in, year out.
That's not to say the latest frameworks aren't all great, if you're building something for a million users and want to take advantage of shiny new features that's great, but for those that aren't, there's still a place for boring old things in a large part of the computer industry.
I'd never say don't use jQuery, and it does support some options for a minimal footprint, still there's smaller options that probably have all you need.