"You are morbidly obese." "You are so tiny I feel like I'm crushing you." "You act like I'm your last hope of ever meeting a girl." "Your religion forbids premarital sex and that won't work for me." "Your conversation is just really boring."

All but one of those are things that people can change. The most difficult one to change (being tiny) is something which people can adjust in part by bulking up and also carrying themselves better. Frankly, speaking as a really tiny male homo sapiens (slightly under 5'2) , if I were to ask someone out and to find out that that was the primary issue I'd be a bit relieved that it wasn't something else. On the other hand when I was told explicitly that people were not interested in me due to my height it has sometimes felt really awful. But it did cause me to focus more on people who were of below average height or not too tall and that seems to have lead to some success. So even that has been a general positive.