Since I'm a sociologist* and all, I figured I'd throw my theory out there. Long-term marriage requires love, respect, and trust. This we know, right? There are even songs and psalms about it. Here's the thing, though. There's another massively important ingredient that is completely squashed in a reality-show environment: the ability to LET THINGS GO.
Say your spouse does something that bugs you... I'm just going to pick something at random... like, using paper towels to blow his nose instead of walking three feet to the box of tissues on the table and grabbing some of those. And when you go to get a paper towel, there's a lonely cardboard tube, but no towel. So you go to the pantry to grab a fresh role, only to find that the entire stock of rolls purchased for the week are gone.
In real life, you say something like, "Could you PLEASE not use the paper towels to blow your nose?" He says, "Oh, sorry." And that's that. In reality life, there's probably a montage of every time he's snatched a paper towel throughout the history of the show, and then when you go to the grocery store to get more paper towels, perfect strangers say, "I see you're buying more paper towels. I can't believe that your husband uses them to blow his nose!" And then you get annoyed all over again. Even if he changed his habit, the audience would still think he does it, and then that would grate on HIM. And because of the commentary, the couple feels like they need to put on an act and behave as if everything is OK, because then maybe everyone will think everything is OK, and then maybe you can work out your issues in a semblance of privacy without dealing with people asking if everything is OK.
Suddenly, these silly roommate issues become much bigger deals because entertainment and its composite parts never really allow the water to wash under the bridge. To continue the analogy, the water pools in a dam and eventually either washes over in a torrent or breaks through the cracks.
I know, I know, most of the time the couples involved say that the end result would probably have been the same, but that the reality show caused them to get there faster. And I doubt that anyone's marriage has ever reached the crisis stage because he leaves the toilet seat up or she never puts her clothes away.
But how do you know? I knew a woman who actually questioned her husband's love for her and commitment to their relationship because he continued to put dirty dishes in the sink when she had expressly requested that he not do that.
Ultimately, I think we all need to be able to just ignore some things, pretend he doesn't do this or she doesn't do that. Plausible deniability is also clutch. Filming your life allows for neither of these things.
*I have no degree in this subject area. I know people who have Ph.D.s in Sociology, though, so that qualifies me, don't you think?