> it'll be silly to spend so much effort testing it in India and Middle East and then not certify it there, right?
Interop testing is very different from certification! Costs, paperwork, lead times...
> buyer will go and get it from customs
Nope. That only works _of the customer is at the port of entry!_ and in many cases custom will not release it.
It is simple. If you don't do certifications and related paperwork (ie: recycling for EU) you will have devices held up at customs. Maybe some get through, but it's an expensive bet to take.
The companies you list seem to be manufacturing in China and selling in China. That's easy -- only one market to certify, and planning to make and sell in large scale.
What is hard, costly and time-consuming is certifying and doing all related paperwork for many different countries. It makes sense if you're planning to sell a large number in each country you certify for.
And some countries/regions are just complicated and expensive. For example, electronics are expensive in EU... and now I know why: the manufacturer/importer has to pay a significant recycling fee and make arrangements for recycling. The barriers to entry are very high.