The absence of clothing among reported alien sightings could be attributed to a variety of factors. Firstly, cultural differences play a significant role in how individuals perceive and utilize clothing. Just as human cultures vary in their clothing norms, aliens may have entirely different social norms or may not have developed the concept of clothing at all. Secondly, the biological makeup of aliens could contribute to their lack of clothing. If they possess different physiological features or skin compositions compared to humans, they may not require clothing for protection or modesty. For instance, their skin might offer sufficient protection against environmental elements or regulate temperature differently. Moreover, advanced technological capabilities might make traditional clothing unnecessary for aliens. They could have devised sophisticated materials or personal force fields that fulfill the functions of clothing, such as providing protection and privacy. Lastly, environmental adaptations on their home planet could influence their clothing practices. If their planet has a stable climate or if they have evolved to thrive in extreme conditions without the need for clothing, they may simply not perceive the need to wear it. In essence, the absence of clothing among reported aliens are variables of culture, biology, technology, and environment in shaping perceptions and practices related to attire. Or simply nudists from outer space intelligent enough to not wear clothes because it leaves fibers that are physical forensic evidence and they don't want to be detected. Grey aliens in particular are not anatomically correct, no reproductive organs or digestive tract ending in a sphincter so they have nothing to cover up with clothing for a modest reason. Either clones or biological robots.