The Amiga 1000 came out in July 1985. This was an era in which personal computers were designed by their manufacturers to meet a unique set of bespoke requirements. For example, some computers came with advanced hardware for sound (for the time), while others had very primitive support for a "beeper".

It seems reasonable to conclude that personal computer buyers of this era tended to choose a system that focused on the hardware/software features that they felt were important for their own "use cases". Again, using the example of built-in audio support, a musician would be inclined toward a machine with more advanced audio capabilities. So would a gamer.

My question is what sort of use cases in 1985 led buyers toward purchasing an Amiga, and why would it be a better choice for those particular use cases than the PC, Macintosh, or Atari ST?