A planet stereotype is a kind of planet whose whole surface is covered by the same biome (kind of landscape). These unoriginal planets occur frequently in science fiction, particularly in bad SF. Such planets include the
The reason why these planets are so simple is that most of the time, we only see one or two places on the surface of the planet. So there often is no need for a planet that is worked out better than a simple stereotype. There are exceptions to that, of course. Realistic planets are a part of good, hard SF.
An example of an excellently diverse planet is Hyperion, from the book Hyperion by Dan Simmons.
Of course, an author can also take a stereotype and add enough detail and sensible explanations to make it interesting and realistic. Frank Herbert's Arrakis is probably the best example.