I want to know why the phenomenon of moore's law exists - why double every 2 years?
Moore's Law doesn't decide anything, it's an observation and a prediction. Has tended to hold true for quite a while though, but now we're expanding sideways instead of upwards (more cores instead of higher speeds).
Read more about Moore's Law on Wikipedia
Oh, and in the future, try to write better questions. I assume your question means the same as "Why is Moore's Law written the way it is". If not, please rephrase it.
Seriously, how hard can it be to get the markdown server-side renderer to work properly? I had to edit this answer 6 times before getting the link to show.
From Wikipedia :
Although Moore's law was initially made in the form of an observation and forecast, the more widely it became accepted, the more it served as a goal for an entire industry. This drove both marketing and engineering departments of semiconductor manufacturers to focus enormous energy aiming for the specified increase in processing power that it was presumed one or more of their competitors would soon actually attain. In this regard, it can be viewed as a self-fulfilling prophecy.