Why are you being such a jackass with your replies? You asked an ambiguous question not really relevant to the article, people are trying to answer, and you're attacking their answers for not addressing the exact meaning of your question. Do you want answers or not?

Maybe if you edited your original post to better explain the answer you're looking for, someone could give it to you.

My own guess, as not-a-physicist, is that physicists expect the predictions made by existing science and their hypotheses to eventually be observed through experimentation. Given what we know, we can predict that some particles/types of particles should exist; projects like the LHC are created to test these predictions.

Or to put it simply: physicists might expect an upper bound on particle types because the available science doesn't suggest there should be an unlimited number of types of particles.