A lot of it also comes down to where Hasbro were trading, where they had offices or subsidiaries. If Hasbro traded [had an office base/distribution network/sales forces/etc] within a country then they would easily be able to simply use the same factories and processes as Hasbro US did; hence why you get UK/German/Dutch exclusives which were only out in certain countries [in some cases classed as Nirvana] but were made in Hong Kong and China. Hasbro UK or Hasbro Germany would simply work as their own business, create their own lines, pick and choose from US designed lines and order anything they wished for their market from the Far East Hasbro factories.
In countries where Hasbro did not trade or did not have a commercial base it made more sense, and more money, to simply license the line to other local toy manufacturers. Why miss out on a market place just because they did not trade there - provide moulds and contracts and get your money by just doing some paperwork. The licenses would typically restrict which countries they could be sold in, in order that they did not impinge on existing Hasbro markets. Although thanks to DAG mainly there is some cross over in a lot of central west Europe.
As to why they are different variations, that is down to factories and choices by the toy company. The licensees would have been provided with licence documentation - this is literally a list of ponies, the colours they should be, close ups of their symbols, their names and many other details [however no actual mention of pose or species]. Back in the 80s we are not talking something as helpful as providing a computer file with vectors and detailed images. They were normally a few A4 pages which had to be recreated from paper. I think in those circumstances and with language barriers, its not really all that surprising so many countries have so many ponies which are variation of their original releases.
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