A lawyer commenting on the game industry (which is largely copying the Silicon Valley business model) has an excellent explanation of these cycles, and why it is that the industry is simultaneously reporting record profits and mass layoffs: https://www.youtube.com/watch?v=-653Z1val8s

tl;dw (in my own words): investors like it when you have extreme hiring during the good times, and they like it when you have extreme cutbacks during the bad times. Investors don’t like slow and steady growth.

Interestingly, Nintendo quite firmly rejects the Silicon Valley approach, sticking firmly with the slow & steady - and while the rest of the games industry was doing layoffs, Nintendo gave all their employees 10% raises.