It might be because anxious attachment is a way of describing the way some people connect with others especially emotionally significant others in their lives, Individuals with an anxious attachment believe they’re flawed, inadequate and unworthy of love.
Some infants perceive their parents as inconsistently available, which distressed them (understandably so, children need their caregivers for their very survival.)
When kids become distressed, their parents may give them extra attention. These kids also may receive attention when they meet others' needs.
Over time, they develop a characteristic sense of feeling needy for attention and needing others to help soothe them. They believe they aren’t loved for themselves, but for what they do for others or how they respond to their needs.
Naturally, such beliefs negatively affect their relationships.
Because you are picking a certain type of guy, there aren't that many healthy secure guys around, or the way you behave makes them insecure.
What I've found is that we are attracted in the sub conscious of our minds to a large extent. that attraction is rooted out of childhood somewhere in our fathers and mothers or some model we had of man/woman. Often it isn't good. So if dad was a weak insecure guy, that is comfortable in your sub conscious mind and you select those guys. It works that way until work is done to make changes.
It is possible there aren't that many secure guys around... too many people get married and date... and end up hurt... and don't take time to heal and learn and develop. So they are rebounders and they are insecure from their prior wounds.
The other point is how you handle yourself around other people. If you are an extrovert and flirtatious in your behavior, you may be making them feel inecure around you. That may be an outcropping of your own insecurity. It would be natural for most guys to be threatned if you flirt with the waiter or guys that pass by, others at the dinner table, etc..
I would say it goes both ways just that we tend to notice it more in the group we are attracted to - Why, I don't honestly know, human nature - I suppose since we all have some insecurities, what is important is learning to handle them, shove them way to the back of your mind and don't let them take over.