Why do I say so? - it is obvious. With out evidence a 'theory' or speculation as to a purpose for life is just a guess, or a wish, or a hope. It is not founded in reality, just ideals. Examine the facts and they do not support the theory.
It has been the creation of a theory or ideals without verification that clouds thinking. Start with a theory, look for experimental evidence or verification. It is exists, fine. If there is no evidence - throw out the theory - for it is WRONG.
We exist; we can find / make up our own purposes; we can speculate and project purposes; but in actuality - none (at some higher level) exists.
I see no problem with that line of reasoning. I see wholesale problems with the assumption that life has a purpose that is based on myth or assumptions that can't be grounded in reality or facts.
If your thought is that the purpose of existence is to allow humans to find their own purposes, well that is nonsense. There is no purpose to existence. Second point (but not connected to the first) is that was can find our own personal purpose - but that is not the purpose of life - just an outcome.
Existence does allow us to find our own purpose - but that is not the purpose of life or existence.
Most people in the world can't accept that reality - so they make up the theory (or simply accept old popular theories - same thing) that god exists. They create god - not the other way around (that god created them). They create a belief system that god exists, has some purpose and created life. All nonsense and theory with no facts or reality to support the notion.