Wife’s Secret

After two years of marriage I thought all was well until my wife let down her guard. While fooling around I was fingering her and she kept pushing on my hand until I was knuckles deep, she orgasmed very hard and as I started to pull my hand away she grabbed my wrist and slowly pushed my entire hand inside her. After a few deep breath’s she began to rock on my wrist and in seconds she was getting off again and again. She was so aroused she started to tell how much she liked sex with a big cock. I don’t need it all the time but sometimes I just need to get fucked. Then she told me about her FWB she had when we met.
I remember when we first met and she wouldn’t have sex with me and when we finally did when she got on top she kept raising up too much and my dick would come out. She became frustrated and I felt she had been used to larger. I actually asked her afterwards to which she said mine was perfect.
Once a dildo was brought into play after we married it was clear she had much faster and bigger orgasms on the larger dildo. While I was maybe getting 7 inches in her the girth was driving her wild. Seeing her orgasm like this was very erotic but all I could picture was her with some other guy.
Why would she marry a guy with a small to average penis when she clearly prefers larger?