It is possible to fix UI problems without people noticing. Also, people quickly get used to suboptimal UI and all kinds of UI bugs. Fixing those bugs improves

It is possible to fix UI problems without people noticing. Also, people quickly get used to suboptimal UI and all kinds of UI bugs. Fixing those bugs improves the experience for new users while acclimatized users will be indifferent or even hostile to the change. It's a classic dilemma for long-lived products.