Looking at the timeline data tables here, it's not like 99% get oath Same day. Pretty much everyone has to wait anywhwhere from 2-5 weeks. Then there are some of us who have to wait longer. My oath ceremony is about 8 weeks after my interview eg.
To be clear I wasn't approved in the interview and was in limbo for a while till I recieved a phone call abour approval and oath location a few weeks after interview.