The value-add point is the key. A lot of countries that are stuck in the trap are still producing low value-add products. In particular, the countries of SE Asia still have a large agricultural and tourism sector, which don't produce high value-add goods. Countries like Thailand and Vietnam are trying to move into high-end manufacturing but Thailand is struggling.
China is a curious mix - it has high end products, but a great deal of its output is based on low-end, low-value products, hence it's still stuck in the trap.
It requires a lot of institutional preparation, arrangement, socio-economic prerequisites, and promulgation of certain economic policies in the right place, and at the right time, for a country to successfully transition from an agricultural-based economy to a high-end manufacturing one. Very few countries were able to pull that off.
Well in China's case it's also just a pure numbers game, their middle class is sitting at about 600 million people now and it's hard to envision any kind of world where there are that many well paid white collar jobs to go around, regardless of what policies the government might institute. But this is different from the standard middle income trap, because even as China's labor costs are risen, it has been able to retain most of its industry because their workers are still more cost-effective in terms of productivity per dollar than those in either richer or poorer countries, as American and European workers are marginally more productive but vastly more expensive, while workers in India, SE Asia, or Africa are cheaper but only a fraction as productive. It's just that the current generation of skilled blue collar workers is being replaced by a generation of aspiring white collar professionals who don't want to work the same factory jobs their parents did.I'm not denying that. But all those things can be put into place - it can take a long time, but it can be done, if the political will exists to do it. It's not something that can be done all at once if the prerequisites aren't there. For one thing, you need an educated workforce that's able to sustain those institutions and economic sectors, and not all of those countries have that. Or some of them do, but accessibilty isn't sufficient (and if you rely on the private sector to provide it, will never be).
In China's case now, the skills are there but the jobs aren't. A few decades ago, it was the other way around.