The question is whether or not the reasons are adequately explained by simple statistical fluctuations of the sort that are always present (like flipping a coin, every so often you'll get a run of 5 heads, etc.). Or is there some other underlying thing going on? The
null hypothesis is that simple statistics explains the fluctuations. The "hot hand fallacy" (which may or may not be a complete fallacy, see the Wikipedia article, but has been long considered such) is that there is something else going on. But to disprove the null hypothesis you need empirical evidence. You can't just say "it's so because it's so". At least not if you want to have modern mathematicians and scientists take you seriously.