Is it because for every american their only choice to get any retirement or any interest on savings is to put it into stocks? Followed by massive speculation that maybe (I dont know this part) is driven by machine code that not only follows trends but creates them by thinking if everyone is investing and line goes up, maybe this is where the money should go, which reaffirms the algorithm. Until it doesn't.

Surely these two things are a factor. That and companies continually laying people off, or cutting costs, or selling data which give the illusion of making money when really it's just juggling the books and has no long term future.

Sure there is. It's a pyramid scheme. It'll work until it doesn't. The people involved are just really good at moving assets around to give the illusion that line keep going up. To keep it growing they move assets from other safer markets (pensions to 401ks for example) and have lobbied to not be taxed or regulated so more and more capital gets dumped in. But stocks aren't tied to anything more tangible then trust of the people holding the stocks. So long as the stock holders believe stocks are valuable they are. But like any good pyramid scheme eventually they will run out of suckers to bleed for cash and then BAM pyramid fall down.