It's a very good question. You have asked a genuine question but I think it can be a great rhetorical question. I feel like developers nowadays blindly learn these "new technologies" just for the sake of learning new technologies, even though they will probably never build anything that really need these technologies. Maybe you get some street cred for knowing more but if I were you I would rather spend my time and energy actually "building" and experimenting things than just learning some esoteric technology that you probably don't even need.

Probably not the answer you were looking for, but I can't help but think it's pathetic how developers tend to think they're competent at what they do just because they know how to use the latest popular build tool, deploy tool, and some new framework that you probably will go out of fashion in a few years. (I'm not even exaggerating. Coffeescript used to be the "it" language but not anymore, people used to rave about grunt, then moved on to gulp, then webpack. Probably next year it will be something else. Same goes for Backbone => Angular => React hype cycle, you get the point.)

Just to share my two cents, you mentioned knowing these "React", "Kafka", and "Heron" will get you a better job, but that is far from truth. Let's say a company is hiring a frontend developer. Chances are they won't hire just because you know React. It is assumed that good developers can just pick up any new technology and learn quickly so just knowing some trendy technology won't make or break anything. They will probably test you to see if you have fundamental "vanilla javascript" capability.