It's not skepticism, it's experience and real life.
I personally think that's why a lot of well-meaning Christians wind up divorced. We all want a God-focused marriage with two people devoted to their faith--that's a no-brainer.
But then real life happens. For instance...
1. Your spouse wants to spend money on a new computer or new phones, but you don't. You want to get the car paid off early, but your spouse thinks, "We have all the bills paid this month, any other money is for play!"
2. You suffer a miscarriage as a couple, and you want to try again, but your spouse is heartbroken and does not.
3. You have to decide what to do over caring for an aging parent--put them in a home, or take them into your own home together?
4. Your child is having problems in school. You want to get them a tutor but your spouse says everything is fine and that your child is just going through a phase and will catch up.
God isn't necessarily going to say, "YES, GET THAT CHILD A TUTOR AND IF YOU DISAGREE, YOU ARE SINNING." And these are just a handful of a thousand other things that will come up when you get married. I think many Christians seem to think, "Oh, God will take care of everything!" and He will. It's just that if you don't have any way of compromising on very important life decisions and haven't thought about how you'll deal with it when you have long-term disagreements... or won't always get your way... simply saying, "We'll trust in the Lord," is bound to set you on a course for the Family Forum... Generally under a thread title of, "My Spouse Just Doesn't Understand," or "My Marriage Is In Trouble." I think many Christians are shocked to find themselves in a place of constant disagreement, discord, and disillusion all because they truly believed all they would ever have to do is "just follow the Lord."
Even church service can become a point of tension. What if your spouse wants to spend 4 nights at church but you feel as if you already never get any time together? I had a mentor once who was always trying to take people into their home but at one point, her husband (and they were both very devout Christians, leaders and elders in the church) put his foot down and said no. She was convinced God was calling her to do this, but in the end, she felt it was best to obey her husband's lead and cut back on offering their home to others. (At the same time she felt God was leading her to take people in, he felt God was warning him about some of the people she was extending this hospitality to.)
What would you do if you feel God is calling you to do X (spend more time at church) but your spouse says No, I want more time with you! Would you accuse them of keeping you from following God? Would you expect them to sacrifice their needs to allow you to do what you feel God was asking you to do? Would you go ahead and do it anyway even against your spouse's wishes? Would you then be tempted to look for a spouse who was "more Godly"?
If life were always cut and dry and A + B always equaled C, then yes, these simple answers would be enough.
Life, however, is usually not all that simple.