Bubbles and their popping happen because of the introduction of radically new technologies. Everyone knows that the technology is promising in the aggregate, but no one yet knows how. That is what entrepreneurs have to sort out. In the 1980s the personal computer was worming its way into society, just as the Internet was in the late 1990s. (In the 1920s, another famous bubble, it was electricity, radio and cars.) In the 1980s the Reagan tax cuts unleashed a lot of stock-market experimentation, further pumping up the bubble. These are unavoidable events given certain kinds of technological developments.
The 1987 crash was arguably a momentary pause in a boom that has been going on for over 20 years.
Well, there's also the complete reworking of credit deductibility that also caused the S&L crisis.