Like many valuable resources they are valuable in large part because they are scarce. Qualified teacher trainers are no different.

My feeling is that the market for language schools in China is beginning to change. You can already see it changing in some of the bigger more cosmopolitan cities and it is at least in my opinion the result of two factors

1. That in general the Chinese are becoming more consumer savvy - they expect better service and product for their money

2. There are an increasingly large number of young people who have studied abroad returning home with very different ideas from their parents not just as consumers (as noted above) but also as the next generation of business men and women.

I met a young (30ish) entrepreneur not long ago who had invested in a language school. He had spent time studying at a highly renowned British uni then worked for several years in the City. We spoke about the current state of language schools in China and i expressed my belief that most of them place education as a secondary importance to sales & marketing. When i asked him his opinion on this he told me that his ideal business model was a school that didn't need a marketing department but relied entirely on its academic reputation i.e. the quality of its product/service to entice new business to the school.

This to me sounds more like a place that qualified teachers and/or teacher trainers would like to work in.

Where are they now? Well they're not (for the most part) working in private language schools in China that's all i can tell you and who can blame them. If you were a qualified professional would you want to be told that your skills were of secondary importance? McDonalds and Noma (a famous Danish restaurant) are both restaurants. Which one is likely to have a Michelin Star chef working for them?
In short, those schools that can begin to act like schools and put education first will attract the limited number of trainers that there are. The rubbish schools will still exist but you'll see a more developed market with options (at least for those with the cash) as to what kind of and quality of product you can buy.

Another consideration could be to see more local (Chinese) trainers take the positions that usually require the training of junior teachers e.g. Director of Studies. Why rely on sub-standard foreigners for the position? A foreign expert should be just that.

Furthermore, there is always the possibility of outsourcing your training. I'm not actually aware of anyone taking this option although i have heard the idea before.