Because people have a lot of very personal ideas, knowledge, and states of character that can't be communicated to their real-life peers, either because it's deemed too outrageous/embarassing in their view, or because they wouldn't understand the technicalities.
However on the Internet, everyone is relatively equal and knowledgeable at the root, so it provides a outlet along with a benchmark for these secret idiosyncrasies. As this is a baggage of ideas that can become an emotional burden if ignored for too long, people tend to try to stand out and entertain others as much as themselves to stand high on these splinter human groups, and to relate positively to likeminded humans, as well as to charm the more ignorant ones to what they are in spite of their prejudices.
Psychologically for oneself it's important to establish its natural ideals and abilities highly (or just fairly) on some social pyramid with castes including people of lower, normal and higher importance to mentally herald an easily recognizable form of comforting superiority and value. People then subconsciously feel safe in the secret garden of their psyche when being in the real world with thoughtless people alien to their very essence.
