Originally posted by DrBong
I think the reasons mostly boiled down to money and convenience. The Atari ST was a larger games market for most companies in the 1980s than the Amiga simply because the ST was a significantly cheaper computer to buy than the Amiga back then. This was probably evidenced by the fact that games on the ST were often at least 5 UKP cheaper than the Amiga ones, even for the same title.
If selling to a smaller market wasn't a factor, then development costs and convenience probably were. I imagine it was more economically viable for a game to be published on the Amiga if it could be conveniently ported across by the ST coders without having to spend too much time doing so. For the publishers, this meant that a separate Amiga team of coders didn't have to be paid, and there was less financial risk involved if actual sales fell significantly short of projected sales in the smaller Amiga market.
This was an interesting explanation, thanks.
BTW, I never noticed that there was already a thread listing some "unreleased" games...