> serious question. Back in the 90s viruses were huge business,

No, they were not. They were toys written for fun and/or mischief. The virus authors did not receive any monetary reward from writing them, so they were not even a _business_. So they were the work of individuals, not large teams.

The turning point was Bitcoin. Suddenly it provided all those nice new business models that can be scaled up: mining, stealing cryptowallets, ransomware, etc.