[SmG ZzigZag]

Money, a stable job, medical and educational benefits, a good start to adulthood, provides you with tools and skills, some want to take a life, some want to serve, some people do it to get off the streets. There is a multitude of reasons why people join, however, staying in or re-enlisting is beyond me other than if you have a family to support.

This 

Many countries military have job training and job placements in the military which also have civilian counterparts
Some jobs suck 
Some jobs are kick ass 

Plus educational benefits and earning credentials
 
And military experience and security clearance are pretty valued (e.g defence contractors)
And the allowances as well 

Sure drills can be unpleasent and PT can be too 

But that's military !