I can only make some assumptions based on what others are talking about and things happening here for some time.

1. It's something to do with the clap-and-run habits of readers. I think it's increasing with time.

2. It also may be because Medium did some intentional tweaks to their algorithm to reduce money out while money in is increasing. More profits?(This would be the worst and last thing though)

3. Many people have been revoked in recent times. We may have also got most of our reads from them. Some may have engaged genuinely and aggressively too.

4. Recent bans and suspensions lead to a fear of engagement among writers, making them spend more time writing rather than reading and engaging.

5. Increasing external views that don't pay?

6. Decreased EPR due to the type of readers who read your stories. FOM or Non-FOM, variable number of claps by them.

What else can it be?