It is easier to be out of shape than to work out regularly.
It is easier to sleep in on Sunday morning than it is to gather up the children for church service.
It is easier to a "C" student than to be an "A" student.
In short, laziness.
One of the wisest things I have ever heard is that over time, you learn that the "easy" way is really the hard way, and the "hard" way is really the easy way.
This applies to just about everything in life.