Perceived high-potential-margin businesses with lead time lead to speculative investment in low- (or negative-) margin businesses in the same field with perceived potential, which is sensitive to fluctuations in the broader investment climate (e.g., payoff timelines) or reassessment of profitability potential. That’s what the dotcom boom and bust were about.

The actual high-margin businesses wouldn't be taken out in the bust unless they were high margin only because they were selling into the boom.