She has a low self-esteem and these are the guys she feels she can get, and by being better than them it makes her feel better

or

She has a controlling personality/subconscious and feels the need to "parent" her significant other, so finds those in need of it. May also stem from feeling like she doesn't have control in her own life and feels the need to do it to someone else

or

She has specific hobbies and spends a lot of time with people in that social circle, and those hobbies are frequented by guys who fit that description. She chooses them to 1.) have someone who likes her hobbies and not taunt her for it, 2.) They are close-by and quite frankly, safe. 3.) She might be shy and is only comfortable in that social circle. 4.) Because of the seclusion in that social circle, she doesn't know other options