The reason is very likely to protect you from being independent, strong and in control of your own destiny. Those things require constant growth. And taking full responsibility for yourself and your feelings. And being willing to take risks. And letting go.
Limiting relationships are an insurance policy.
They insure you against the truth. Let's go back to the kitchen table where that little scene was unfolding. We have a lot in common and I think we're going to be friends. Among other possibilities, your partner might lose it and create a very uncomfortable scene, in which case you might have to ask yourself why you were in a relationship with them at all. A swami whose work I respect greatly equates this very experience with the primal terror of death, and says that's why jealousy is so shocking - and such a powerful learning tool when we face it and don't shove it away somewhere.