This is absolutely going to fan the flames but I'll throw it out there anyway.
Among C girls (can't really comment on the others), both in shops and out, there's a general perception that Asian people are inherently cleaner than, well, anyone else. This is specifically East Asians, not the brown ones like Filos and Indos and especially not Indians. For the few decades I've been an ABC, I've found this to be the case although I have found that this sentiment has grown in recent years.
This is not really related to perceptions of dick size in the way that this thread has been implying. It has to do with a perception of vulgarity and a way larger dick is perceived as vulgar. Bodily hair and natural bodily odour all add to this perception. To compete against this baseline perception you're going to have to be outstanding with your looks and, probably, your wallet. For East Asian guys, the bar is set a lot lower in terms of what is acceptable.
In your daily life, sure, you'll meet the occasional open minded C girl. You'll also meet curious C girls. However, you probably met them because they were open minded or curious. There's entire suburbs of Chinese people in every state who haven't learnt English over the many years they been in the country. The percentage that actually pursue relationships outside of East Asians is incredibly small.
When hitting up a shop, that's a social interaction that wouldn't happen if they weren't at the shop. A few of them have suddenly realised they have the ability to get picky with a static supply - supply and demand as people have said. They probably asked themselves if they'd rather make 1.5 a day and feel really icky or 800 and feel a little icky.
Feel free to hate me if you want but I thought I'd share that based on what I've noticed. I don't like dick - white or East Asian - so it's not my opinion. I'm also down to fuck all races whether I'm paid for it or not
.