Are divorced after a long marriage and, having taken time to collect themselves, are now "on the market", but encounter issues dating if they have children from the previous union or if their divorce was messy. 
If combined with the previous explanations, oof.
Are the "odd one out" in a community, such as an educated professional residing in a rural community which tend to be more Conservative and evaluate postsecondary education as unnecessary or even detestable. If combined with the first point, the situation is exacerbated ten fold.
Are transplants to an area, meaning they have no local social circle and are starting from scratch. Work in fields that are gender stereotyped, such as education and social work, where meeting men is uncommon or, if it occurs, they are already married / it would be inappropriate as they are a client or a parent of a student. Some other explanations for why they may be on dating apps despite being successful people: