Ends-up-in-the-same-place is a hiccup. Until 30 days have passed after March 31, the tail of March's graph will be skewed down. It seems like it will end up quite higher than prior months, although still much lower than the first half of the curve.

So the question remains - why is March so high? My hypothesis is that it's due to Nostrica.

It took place on 19-21 March, some people arrived 2-3 days before that, some kept discussing it 2-3 days after, so overall the hype around the event would last for around 10 day.

That's close to the length of a retention bump (it's 13 days).

Maybe people who started using Nostr before/during the event just joined the hype, and kept being more active for a while, and it all averaged to this bump on the curve?