We just can't think of any new ones, yet.
Sometimes I think everything is simply regurgitated blather...or a cliché...
It is impossible to know if all ideas have been exhausted
Sometimes I think this is true.
Because there ARE original ideas. Otherwise, i wouldn't be a writer.
some people don't have good ideas
While new ideas are rare, original ones are not. Through discovery our knowledge grows; hence, new /original ideas are probable
Something "new" always has a piece of something that came before it in it, if that makes sense. An idea will always be brought upon by something else. And when it comes to thinking in general, if you've thought of something, there's a good chance that the very least a few other people on the planet have thought of that same thing as well.