They don't always all line up in time. Companies grow and die all the time.

Trends, Hypes and Bubbles are probably a consequence of human nature: most investors have a deep fear-of-missing out, so in general money loves to jump on the hype-train. Likewise, fear and uncertainty easily spread: markets moving together. When a couple of businesses fail, that insolvency or illiquidity spreads to related businesses.

Booms and busts have cyclic effects. Booms provide more capital and credit that can be reinvested and beget more booms; busts collapse demand and can contagiously bust other sectors.