A couple of reasons I guess
Kev - if someone found themselves in Sao Paulo for other reasons at some point in their lives and discovered the SP world down there, they would understand. It is indeed far flung and at least two flights from BC but, hey, he asked the question and that is my experience.
The combination of beauty, attitude, lack of "agenda", seeming inability to tell time and an understanding of how to get the male of our species to understand fully why life is worth living is some of it. The cost of a good meal out in, say, Vancouver will get you a week in many cases....another good aspect. Finally, very clean, extreme health awareness and lack of the things that can cause concern in the, ah, "business". I guess it just all adds up for me.
Each to their own. Most North Americans go to Rio and pay WAY too much for chichas and worse. If anyone is heading south, don't forget Sao Paulo!