Openness is a major driver of Evaporative Cooling. If anyone can join your community, then the people most likely to join are those who are below the average quality of your community because they have the most to gain.
Twitter Blue feels like a missed revenue opportunity.
People don't pay for features. They pay for social capital and status signaling.
Twitter could 10x the monetization potential of this by adding things like paid verifications, badges and profile page cosmetics.