I can't find the original survey but Sage did apparently look at why 50 year olds were divorcing - it's referenced in a lot of articles-
https://www.dailyrecord.co.uk/lifestyle/family-relationships/saga-divorces-on-the-rise-as-over-50s-couples-1073229
Figures show that 28 per cent said they divorced because their partner was emotionally cold and distant, while a quarter cited a loss of interest in sex. In addition, 27 per cent said they were no longer committed to their marriage.
The main reason for men ending their marriage – cited in a third of cases – was a lack of interest in sex, while most women said their husband was ¬emotionally cold.
I can't think why couples with out kids would suffer these issues less - maybe they find them earlier with no kids to distract or blame. Though some of the other reasons I could see affecting parents more:
Nagging also scored highly, listed as a top reason for a split by 14 per cent of the 1900 divorcees aged 50 and over asked. In 10 per cent of cases, couples said they'd simply run out of things to talk about.
You get used to oragnising everyone - and then kids leave your left with an adult who resents it all being focused on them - or you drift apart and don't notice.
(missed a word changes sentance meaning)