Despite being a paradigm created a long time ago, why did it begin to be so discussed and used recently?
Because a few years ago the trendiest thing ever was to realize a full MVC architecture in JavaScript in the browser, it was the only modern way to build ;) So naturally a few years later we need to switch paradigms entirely.
Do you think we'll still be praising FP in 5 years after we have jumped to something else? ¯\_(ツ)_/¯
It's (in part) because concurrency has become so important. Functional programming makes concurrency a lot easier, because it minimizes side effects and makes state immutable, which mitigates a lot of issues with e.g. interleaving and race conditions.
This isn't the only reason, but it's definitely part of the story.
I might be wrong, but it's probably because of React.