You have to keep an open mind and not make a blanket statement that all overweight girl are unattractive. Yes, it may be that you did not find any attraction to the girl that you dated, but in the future you may find another overweight girl who does attract you.
Also, for obvious reasons, you failed to say how you define overweight. Many people in the frum community define overweight as a size 12. That is not overweight! That is called healthy/average! If your date was severely overweight, then I don’t think that anyone can blame you.
And, like others have mentioned, you may marry a small girl now, but after girls have babies, their figure changes. Your previously size 8 wife may now be a size 14, just 10 short months after you married her.