"Free will" on the part of the marital transgressor/divorce initiator.
They don't think of it as "God's marriage partner picker is clearly off", and/or "these people were never suited for each other".
Hence the big push in their own households to stay married no matter what. Fundagelical family member of mine is content to be maritally separated until the end of days, cutting herself off from any chance to remarry, because Jesus. Even though her husband is a bum, and most likely only refuses to divorce because he wants to get his hands on her Social Security some day, an eventuality which I have pointed out time out of mind, to no avail.