One major difference is that large parts of the internet are economically viable, and not just driven by money pumped in by VCs and IPOs. Back in 2000, there was little real consumer money going into the web's money cycle. Google didn't even have Adwords back then!
Of course there's still a large chunk of revenue today that is just recycling VC money - e.g. apps advertising in other apps, or AWS which is a huge sink of VC money from other startups. But there is a lot more "end user" money coming in from real people and companies that purchase products and services online. Even if that flow stops, the internet today is less of a ponzi scheme as a whole.
Of course there's still a large chunk of revenue today that is just recycling VC money - e.g. apps advertising in other apps, or AWS which is a huge sink of VC money from other startups. But there is a lot more "end user" money coming in from real people and companies that purchase products and services online. Even if that flow stops, the internet today is less of a ponzi scheme as a whole.