How versatile has Star Trek been?
At its heart, Star Trek is about space. The final frontier and the key word being 'frontier'. Frontiers, by definition, are vast and space is a broad palette.
I think Star Trek has survived so long because people will always be interested in other worlds. A show set on Earth is, by definition, Earthbound. It can't really change that much. Shows that in space can be remodelled almost infinitely because the only limit is the imagination of the writers.
When you have a starship that can travel anywhere in a relatively short amount of time � thanks to warp speed � you � you create a lot of infinite possibilities. You create a lot of different universes and a lot of opportunities for people to become attached.
You also create a lot of marketing opportunities as well. The more aliens you create, the more alien dolls you can sell. The more alien make up and alien history books and alien languages that people might want to learn. It really is infinite.