Why is this? I think one reason is that the two institutions we work for much of the time, the Society for Editors and Proofreaders and the Publishing Training Centre are established training providers whose quality is recognised. Another reason is word of mouth, we have been training for private clients as well as delivering in-house courses for sufficiently long for the word to have got around.
But why go to the expense of flying trainers overseas? Again the quality factor comes into play, but also perhaps that editorial training has been established in the UK for a long while and home-grown options may not be available. Britain has a tradition of 'getting it right' in print that stretches back to Johnson's dictionary. People come from far and wide to attend SfEP's and PTC's day courses (including day-trippers from continental Europe) and the online courses attract students from around the world. So it makes more financial sense for overseas clients pay for one expert tutor to hop on an aeroplane than to send two or more delegates on a course in the UK.
So, Singapore in August beckons. This time teaching an introduction to web editorial skills. The experience will be fantastic, though the humidity may not be.