How many male foreigners are there in Thailand, and how many male Thais? The figure you cite is an example of the aphorism there are lies, damned lies, and statistics. It's like saying 99% of Thais prefer pad thai goong over cottage pie.
My Thai massage lady is a classic example. AFAIK she has never been a prostitute. When she was 30 yo, her husband told her she was no longer attractive, and dumped her. She has asked me if I have any friends who would be interested in a hard-working companion, which she is.
You are correct in saying Thai men are not interested in single mothers, because many are as shallow as a mud puddle. It's a bridge too far to automatically label all of them as bar girls, therefore prostitutes.
The guys who end up marrying their golf caddies, are those women all prostitutes too?