That’s easy. You have some ‘product manager’ or ‘UX lead’ who gets hired. They need to make a name for themself, and keeping the old thing going won’t do that. So you get a big redesign. There might even be some QA testing to see if the new design is more intuitive. There will rarely if ever be any testing to see if whatever benefit the new design brings, is offset by making existing users relearn the whole thing.