The reasons people say can differ to what they think
If you have a strong view on something, and want to convince others, then you do your best to convince them. You tend to give them different reasons to accept your view. Generally, you give them one reason, and if they don't agree then you try another.
So one of the basic things we learn is to give reasons that others find convincing. Say I was trying to convince a workmate to do something instead of me. Say the reason I'm doing this is that I'm feeling particularly lazy. But the reason I might say to them might be something like "I did this last time, it's your turn". So my motivation for my position is my own feelings, but my explanation to them is some idea of fairness that I seize on. In reality the fact that I did it last time has nothing to do with why I don't want to do it, but it is a good way to convince them to do it.
People naturally act like this all the time. Motivations tend to be emotional, while explanations tend to be rational. Similarly, we have a tendency when trying to convince others to look for reasons that they might agree with, regardless of our own motivations.
So what's might point? Well I was reading someone's in-depth theological analysis of what Jesus had to say about divorce. They were reading a lot into Jesus' brief explanation about how you shouldn't separate what God has joined together. They thought this proved that marriage between a man and a woman is a God-ordained institution (it seems to me that a simpler explanation is that this is a reference to marriages taking place with vows before God). But anyway, that got me wondering. They are assuming that the short explanation given by Jesus is his real motivation.
As I noted above, real motivations and the explanations given are often two quite different things. Explanations given are usually ones that the hearers accept, not necessarily ones that the speaker accepts. So it seems faulty reasoning to say that because Jesus gave a certain explanation to his hearers that he not only accepts that as the explanation, but also endorses every single imaginable theological implication of that explanation.
You see, the Jesus I see in the gospels is largely concerned about caring for the excluded, the outcasts and the suffering, and being a voice for those who have no voice. So it seems a little random to see Jesus giving this commandment about divorce and supporting it with an abstract theological claim. I would expect Jesus to forbid divorce in his society for a different reason, as follows. The women in their culture had no rights, and were not legal entities - they only survived by being in the care of male relatives and then husband. Their husband divorcing them would quite likely put them in dire straits. I would expect the Jesus I see in the gospels to be concerned about this, and wanting to prohibit divorce for that reason. Furthermore, a prohibition on divorce for the sake of the woman is likely to have one exception - where the woman has brought it on herself. Namely in cases of adultery, where the woman has dishonoured her husband by sleeping with another man. (Remember, hubsands could not dishonour their wives by sleeping with another woman, because woman didn't have honour. So only wives could commit adultery in a relationship, not the husband.)
So Jesus' statement that a man should not divorce his wife except in cases of adultery [ie where she has committed it], fits perfectly with a motivation of concern for the woman, which in turn fits with the Jesus I see elsewhere in the gospels. So perhaps his explanation that man should not separate what God had joined was a reason for the hearers rather than a motivation for Jesus? Perhaps it was a proverb, or a common reason cited to prohibit divorce which Jesus uses to support his point?
Of course we can't really know one way or the other. My point is really that we should be aware that it is common that the reasons people give aren't the ones they have, and keep that in mind when interpreting the bible. Let's not get too enthusiastic about accepting the reasons given at absolute face value and doing deep theological analysis of them, in case they actually weren't the real reasons at all.