There was once a time when interim titles were rare. The UFC only instituted one for a division if the titleholder was out (usually injured) for an extended period.
It took Dominick Cruz to be out for nearly a year due to surgery and facing another year-long injury absence for the UFC to put an interim title on the line between Renan Barao and Urijah Faber in 2012. Cain Velasquez didn’t defend the UFC heavyweight title between October 2013 and June 2015 and the UFC waited for him to be out a year and pull out of another title fight before dropping an interim label.