You don’t have to be a Chinese company to move production out to China.
The thing is that companies like Aguilar and Mesa are usually privately owned and understand their products and customer base. Of course, they want to make money, but they don’t need to make it all right now and they are just as concerned about their reputation and the continued excellence of their products. As soon as they are bought out by a larger company, their amps are no longer the core business and ‘Wall Street’ rules start to apply – its all about quarterly earnings, short term profits and cutting costs. The parent company understands the brand rather than the product and the new CEO just wants to make quick profits to justify his annual bonus rather than ensure the long-term reputation and viability of the company (in three years time he will have moved onto another job anyway).
I am sure that there are exceptions, but this is why these mergers are rarely a good thing for these smaller high-end producers.