The reason late 90's start-ups invested the way they did is because they had no meaningful way to track the effectiveness of their ads, much less the payback. A Super Bowl ad for Pets.com seems fine if you can (more or less) guess that it adds a bunch of customers.
Since then, start-ups have built a bunch of tools to track customer acquisition costs and paybacks in a pretty sophisticated way, and some of the obviously crazier ads dies (or at least become more one-off).
But now we are in a fintech/crypto era and nobody really knows how to calculate paybacks once again, because the business model is so new vs. a traditional ads or commerce business (will this new crypto.com user do $1k of transaction volume every year for the next ten? sure why not?)
As a result of all this, we see crazy 'spaghetti on the wall' style advertising again, usually focused in the crypto/fintech space (See: this year's Super Bowl). I wonder when the music stops.