Because science is not about 'feelings' and 'beliefs'. A scientist, as a human being, can 'believe' that organic life exists in one form or another on millions of planets in the Milky Way. They can even arrive at this opinion by citing statistics. But it is almost impossible to talk about 'UFOs' in any scientific terms because ALL of the purported evidence that tries to show that UFOs are spacecraft from other planets is anecdotal, and in most cases based on flawed human perceptions and outright deceit. The implication that some UFOs might be spacecraft is so profound that we must demand hard physical evidence, not merely 1000 reports by well-intentioned people. Scientists demand a level of integrity in data collection that non-scientists simply do not fully appreciate. We are not stubborn out of spite or narrow- mindedness. We are stubborn because we know full well how easy it is to create belief systems that have no rational underpinnings based on a few pieces of ambiguous information. We are not trying to uncover laws and facts that make us feel good. We are trying to understand how nature works.