Some of these might also have been hacked blue checkmark accounts resold/reused. Which also was one of the issue with this status symbol, as far as I know the "verification" was a one time event per account.
I think the point is that it’s hard to scale this. I’ve worked in the fraud space for awhile and a big problem is sophisticated actors that scale their operation and cause a lot of damage. If you can make it more expensive to scale, you can change the economics. For example, if it cost 1 cent to send an email, you would probably solve a big chunk of the spam problem.