I guess it's as simple as pretty much everything has been done at this point, same can be said for most things such as fashion, car design, music. You can almost always say that reminds you of something that has come before.
I always consider the 70's as pretty much the last decade of unique and original watch designs. There's a few designs you can recognise as 80's, fewer still 90's but since then it's pretty much rehashed or refinements to existing models.