Software maintenance is a sign of a successful project. People are using the software and they want bugs fixed so they can continue using it in the future. That can be very satisfying for a programmer, even if the application itself is "boring" or not "sexy".

I have worked plenty of late nights and weekends on "cool" projects that never shipped. A project gets canceled. A startup runs out of money. No user would enjoy the fruit of my labor. My code gathers dust in some archived copy of the source repository.