When was the last time a tweet or any other online interaction of yours suddenly had millions of viewers? You're making it seem like this happens all the time.
In reality, while it is easier to broadcast your message to people all around the world in modern times, people still need to "really believe in an idea to help it spread". Unless you're already famous, just because you put it on a platform with potential millions of viewers doesn't mean that you'll actually get millions of viewers without trying really hard.
When the last time _my_ tweet reached millions of users is not the right question. We see that daily tweets go viral and are seen by millions, some things are seen by a billion people (though perhaps not virally in a short period of time). If people are pumping bitcoin with rampant speculation to get other people on the train to increase its value, just a handful need to go viral to increase value, not necessarily yours or mine specifically.
It's like the Birthday Paradox. The chances that someone in a room shares my birthday are small, but the chances that two people in the room share a birthday is large. It just takes a few of the millions of tweets to go viral.
I won't address your second point at length except to say that it's naive to think that with the ease of broadcasting, suddenly the wall is at rebroadcasting, which can be done with no more than a click and is significantly easier than creating the original message.
It's the ultra-modern equivalent of the modern TV soundbite of an off-the-cuff remark. Also a new phenomenon. And it really is a new phenomenon. Until the 20th century, almost no person's expression or idea would reach the global, national or even regional consciousness without having gone through many layers of slowly-building feedback and editorialization and comment. It's like if someone in the early 20th century took random excerpts of someone shouting on a soapbox at an intersection, but published it on the front page of a national newspaper unfiltered. I'm pretty sure no one back there would have seen much value in doing that.
How would you know? The person who got the million views may have copied someone who copied someone who copied from you. You may have originated something but assumed you heard it from somewhere after it caught fire.
The life of ideas and clichés is largely independent of celebrity - if it hadn't been one twitter star that picked up some pithy arrangement of words that fit the zeitgeist, it probably would have been another.
The trying really hard part is just to be in the middle of things, and if you're successful at that, when you're the 1 out of 100 people who said the same thing, you're the one that gets the credit because you have 2M followers.
This is a good point, but it's not the point that matters.
Thee fact that 99% of Tweet are irrelevant doesn't abnegate the fact that millions of Tweets from 'nobodies' are broadcast daily and do impact the world.
Journalists decide on an editorial angle and chose random tweets to support their narrative.
Entire articles are written on random tweets.
You don't remotely need to be 'famous' to have massive social media impact.
In a civilization of self-seeking individuals, the objective of communications will be self-aggrandization there's little incentive in promoting the truth.
I think the blame here lies almost entirely with the "journalists", as they are supposedly the experts with the discenment to know when a an online comment is news worthy (almost never) and when it is not (almost always).
The point of having professions is the expectations that the professionals will be, well, professional.
In reality, while it is easier to broadcast your message to people all around the world in modern times, people still need to "really believe in an idea to help it spread". Unless you're already famous, just because you put it on a platform with potential millions of viewers doesn't mean that you'll actually get millions of viewers without trying really hard.