Because "made of bread" was already taken by Jesus.
This joke makes more sense if you can see it in person, but we'll give it a shot, anyway. Use your imagination. Why do the ladies love Jesus? Because he was hung like this!
I herd that.
It e-loaf-es!
I just need some bread
Made out of bread was taken.
Wartortellini!
Spaghetto Ba-dum tss.