I say my dog is worth a million dollars. You say your cat is worth a million dollars. I trade you my dog for your cat. Then we trade them back.
We've just created 2 million dollars of daily trade volume, err, economic activity.
When looking at value stolen by scammers, what matters is not the daily trade volume, what matters is how much money was put into the ecosystem [1], and what fraction of it was stolen.
[1] Which is a lot less than 180B/day.