Objected Oriented Programming is simply not cutting it anymore, specially when it comes to concurrency and parallelism; trying to add concurrency and parallelism to this languages adds lots of complexity and more often than not leads to over engineering and poor performance.

Functional programming in the other hand is already well suited for these challenges, Immutable state, Closures, and High order functions, concepts that lend themselves very well for writing highly concurrent and distributed applications.

But don't take my word for it, you can find enough proof by looking at the technological feeds of startups like WhatsApp and Discord:

    1) WhatsApp was able to support 900 million users with only 50 engineers in their team by using Erlang.
    2) Discord in similar fashion handles over a million requests per minute using Elixir.