School breaks. Not because many Fediverse users are students but because many are parents.
I’m serious - it has been spring break for many schools in recent weeks (the exact dates of spring break vary by school district) and thus parents likely have been less engaged. Similarly with “ski week” in February (for the parts of the country that have that break) and for the typically longer break in Dec/early Jan.
I know my use dips during family vacations