Because unregistered people exist.
Take nobodyimportant, who first came on KidzTalk in late August 2022, then left on September 11. She came back in May 2023, so Nobi’s active time is 3 months, and she is unregistered.
Also, I was unregistered on KidzTalk for 4 straight months before making an account. And 3 months before I started posting unregistered, I discovered KidzTalk.
That means I discovered KidzTalk in September 2020, started posting in December 2020, and registered in April 2021.