There are lots of reasons that could motivate people to tell lies. Even though each reason might be different than the other, still all of them stem from one root cause, which is being unable to bear the consequences of telling the truth.
Lack of courage, lack of problem-solving skills and lack of the ability to properly handle unexpected events may make escaping from a situation a much better option than facing it.
If the person values honesty and leads life according to the Permanent Values given in the Qur'an, then he lives to escape the situation without lying but if lying is an option and he does not follow the Permanent Values, then it will definitely be considered the easier way out.
Consequently, lying is the combination of being unable to face the results of honesty and the lack of Permanent Values.