I believe that a lot of couples marry because they think it is the thing that couples do.
Friends and relatives apply subtle pressure about 'wedding bells', usually followed by 'the patter of tiny feet', and couples enter into marriage and parenthood without seriously thinking through the consequences of either.
As to being a 'role model' - that strange notion is entirely the creation of the media. No public persona chooses to be a 'role model', it is a label hung on them by the media without their desire or consent, and quite rightly, the majority feel no compunction what ever to adapt and adjust their behaviour based on the perceived impact of a generation of complete strangers.
As Paul McCartney famously told a reporter, when questioned about his 'role model' status, and his 'responsibility' after being caught with dope in his luggage - "I won't tell anyone if you don't - whether or not this becomes news is not down to me, it's down to you."
Marriage is two people, it works if they do, not if they don't, famous or no.,