Were "dot-com" companies listed on the NASDAQ back then, or only companies with significant dot-com investments?
It was the IPOs that drove the boom (and subsequent bust). Public investors falling over themselves wanting to get in on the "next big thing". Older generation companies were never going to deliver the kind of quick return multiples that characterized the boom (though as we saw, the enthusiasm certainly jacked up their share prices too, but by and large they managed to ride out the storm).