>it just doesn't pay off to learn the new, cool thing when it's going to be obsolete in 3 months or less.
Does this actually happen? If you had learned Angular way back, you would still be in a comfortable situation. New stuff coming in, but it's compatible with the old stuff.
Same with React. Had you learned react when it was talked about, you would have gotten, what, at least 2 years worth of value by now?
And a lot of the build tools are independent of the tech. Grunt is still fine to use, and people release plugins for it all the time.
And here's the last thing: You don't have to spend 6 months to learn a thing. If you want to keep up, read about it for 15 minutes? That should be enough most of the time to get the philosophical differences between tools you know. And if it does intrigue you enough, engage with it.
This stuff is progress, if we went the other way we'd still be writing jQuery spaghetti code and having state integrity issues up the wazzoo from callback hell. You don't have to ride every train, but you can at least look at them as they go by.