Most Witnesses get married at a very young age: usually 18 for the girl, although I've seen them get married as young as 16, and usually 20 or 21 for the guy, although I've seen guys get married as young as 18. Now we all know there ain't but one reason for ANY guy wanting to get married at 18: SEX
As for the girls, they get married for different reasons: partly because they believe they're in love, partly because they want to get away from their parents' rules and do their own thing and partly due to peer pressure---any girl over the age of 20 or 21 is seen as an Old Maid. Most of these girls don't work after they're married and they've only got a high school education. They usually have a couple of kids 2 or 3 years after marriage. By the time they're in their early 30s, alot of these couples are miserable but they're stuck. The woman has no skills and hasn't worked outside the home in years; how could she possibly support herself and the kids? Plus there's the whole social stigma within the Borg of being divorced. Half your friends dump you because you're no longer part of a 'couple' and believe me, when you're single, you never get invited ANYWHERE unless you're a regular pioneer. And unless your mate has committed adultery, you're looking at a life of celibicy---and who wants to do that? Even if the wife goes and gets a job, it'll be a sh*t job at minimum wage.
So these Witnesses stay married, not because their marriages are any better than "worldly" people's, but because there's too many repercussions if they got divorced.
Then there's the horrifying thought that if Armageddon comes, you're stuck with this person not only in this life, but for freakin ever.