Looking at the "Complete list of unicorns"[1], something stands out. Out of the top 50 startups by valuation, only three, Snapchat, Pintrest, and Vice, are ad-supported. The others all sell a product or service paid for by its users.
Advertising may have powered the first dot-com boom, but it's not powering this one.
[1] https://www.cbinsights.com/research-unicorn-companies/