Speaking as a veteran of a .com that had $30MM of venture money literally handed to them in 1999 for a concept. No customers, no proven ability to implement the concept, no management that had ever attempted anything like it, etc. The money was gone in a little over a year, frittered away on lavish offices, a huge support organization (for no customers!), massively overbuilt technology infrastructure using the most expensive Sun servers, Cisco networking gear, triple-redundant everything.
Very few tech companies, customers, or investors in that era had any real idea of what they were doing.
I disagree. Where were those banners shown? Search results pages. The reason people went to Yahoo! was to find stuff. That's the reason Yahoo! became Yahoo in the first place. The Yahoo founders made an invisible, scatterbrained web accessible by giving some sort of list index to it. Google later improved the sorting of the index, but Yahoo was first to build a large, searchable index.