Evopsych theories say that males are generally more narrowly focused, obsessive, and tend to solve problems sequentially (A than B than C etc) rather than in parallel (a b and c at the same time).

Could it be a factor favouring oneitis, even in people who are ideologically unplugged and should easily have options?

I.e., is it just quite instinctive and "lazy" to focus on one woman at time, especially when they are "problems" of sorts; while spinning plates correctly would require a degree of work and self discipline?