Why is marriage the most important contract we ever enter into but the least we actively work on to succeed?

Why is marriage the most important contract we ever enter into but the least we actively work on to succeed? We spend more money on improving our skills for work and more time on keeping ourselves fit and healthy than we do in the relationship we are supposed to value the most. Yes I have created Divvito, an organiser to help with separation and shared parenting, BUT I would prefer you didn't become a lifetime member!
Since people can't seem to understand the basics to a good marriage, let's relate it to work since you're there most of the day:
1. You can't stand the coworker who is lazy, peddles off their work to you so they can surf the internet, always wants to do things their way and tells lies to others in the office about how important their contribution to a report was when they did crap all! So are you that coworker in your relationship and you wonder why it's not working out?
2. You can't stand when your boss or manager doesn't listen to your suggestions, doesn't give any praise for the work you've contributed, doesn't even say thank you for busting an all-nighter to hit a deadline. So is this how your partner thinks of you? 
3. Have you ever had to performance manage someone at work? Yet when they are asked to improve they believe it wasn't their fault at all and blames everybody else for poor communication or lack of direction. Upon asking several times to improve and showing no change, they're asked to leave and completely shocked. Then you see their true side. Anger, spite, malicious behaviour and you wonder where that awesome person you saw in the first place went. Sounds familiar to  a breakup you've been through?
4. You have a star performer at work but you've been pretty slack offering your time, praise and incentives because other staff needed more attention. You walk in one day and they say they've been offered a better gig and give you one week's notice with no interest in negotiating. You are gobsmacked and pissed off! Do you have the right to be? Again, this is exactly what happens when you stop paying attention to your partner (and too much on your kids) and someone else starts to. You think you had no involvement in them having an affair but if things were that good at home, why would they leave?
5. If there were unions for husbands and wives and a similar tribunal to the Fair Work Commission, would our relationships be in better shape? 

So before you throw in the towel on your relationship, pretend you're doing a workplace self-assessment to see how poorly you're performing and maybe you should start stepping up before asking your partner to. If you are the star performer, hopefully they are reading this post and they step up to the plate! In any case, good luck and here is to a long, successful marriage!