I don't think toy languages are the a waste of time, because the people who make them improve their own skills. With these skills they might contribute to say,

I don't think toy languages are the a waste of time, because the people who make them improve their own skills. With these skills they might contribute to say, LLVM and all our code gets 0.1% faster. But it's a deeper reason - I don't think it's an either-or between working toy languages and global warming. The choice that I personally face is between enhancing my skills and Netflix/twitch and I suspect that many other people do as well, ie, the choice between creation and consumption. In my opinion, it's absolutely fine to create anything as a hobby if it makes you happy, whether that's woodworking, drone photography, or even reading or watching something that makes you think deeply. It's impossible for us to judge a priori which of these contributions will be useful to society in the long run. So if the people doing it are happy, why stop them?