Aana Jaana!!!

Why do people leave company?

Many reasons can be attributed to  this:

a.)Better pay package
b.)Better Work
c.)Growth in terms of exposure.
d.)Brand Name
e.)Work/area/field/technology is of their liking
f.)Problems at present organization
g.)Peer Pressure

There may be many other but these are the main ones.

Why to stay in a company?

Growth,exposure,money,work...if all are good.
You have reached a comfort Zone and you may be afraid of treading into unchartered waters...
You do not have the wherewithal to give interviews.
You want to settle down and phew...stop this mad race
You are satisfied with what you have..Holistic approach towards life and other considerations to be kept in mind like you are married ,have kids so that
thing will also come into picture.