Dear Melissa,
Sunspots are regions of very intense magnetic field. The magnetic field is so strong in sunspots that it effectively blocks some of the light coming from the surface (although sunspots appear dark, there is still some light coming from them- it's just so faint compared to the rest of the surface that they appear very dark). Although I'm not an expert on sunspots, I think their lifespans probably partly depend on how complicated the surrounding magnetic field is around and under sunspots. Magnetic fields are constantly being twisted around each other since the Sun doesn't rotate rigidly like the Earth, and when they get twisted enough, a flare and/or solar storm can occur. There are many scientists who currently study how sunspots are generated, how they decay, and how they are related to flares and solar storms.
Great question!
Holly