I read on a former Atari employee blog that one of the biggest issue in the US, after of course being named Atari and having to compete with IBM and Apple, was that the strategy "power without the price", did not allow to have a sufficient margin for distributors. Compared to other brands, US distributors and resellers were not earning enough money to invest time and of course money behind Atari. I will have to dig into my links to find the source, but I find this information interesting and quite logical indeed.
As far as Atari strategy to give priority to Europe, it sounds logical : US computer market was more mature at that time than European one ; if you don't know the theory of red and blue oceans, I invite you to have a look at it. Europe was a blue ocean at that time : no big competitors, small level of equipment and strong demand. The price to enter European market was therefore smaller, and when you are a small company, you have to choose your battle.
Once again the strategy "power without the price" had its limits, i.e, if you sell cheap you MUST sell huge volumes to survive, and huge volumes were accessible Europe.
In the 80's IBM PC were totally absent of the European consumer market, busy doing big money in the business segment. Apple were not well distributed neither and very expensive too. The only options were Atari ST, Commodore Amiga and on the cheapest segment Amstrad CPC. Nobody had a PC nor a Mac at home, and in the company only a few used it. Everything changed end of the 80's, beginning of the 90's when PC clones and Windows 3.1 appeared.