Smart phones
Internet
social media, 100%.
Like button.
News Feed.
And the progression of all those things.
Also, texting as the dominant form of communication (because of smartphones), the sheer ability for apps like Facebook, Instagram, Tik Tok, Twitter, Snapchat, to transmit information that rapidly changed communication forever. Nothing could previously reach that many people, that quickly, and without any filter, or time delay, not newspapers, or TV, or speeches, not books for sure.
Then, the platforms themselves incentivize outrage, or attention getting emotional statements. Social media preys on the natural human want to be seen and liked and admired. Forums do that to a degree, likes and daps, and all that, but since we are essentially annonymous, its different, but you still see that kind of behavior at work.
Since mid 2010s like skyrunner1 said, it's been the dominant form of communication. It's performative, and like any new tech, at first people used text kind of like emails, or letters, they used the new tech to improve on the old, which was longer form, somewhat in depth messaging, as the technology progressed and many people adapted, it become shorter and shorter, to where we use memes, emojis, short videos to convey emotions. The main thing is that the phone and all the communications mediums within it, is no longer separate, it's no longer just a communication device, it's an extension of the self.