I think it might be because I separate the creative process into two parts. First, the writing part, where the actual sounds created or chosen on the instruments are not that important. I focus on the actual composition – chords, bass, melody and drums. Then, in the next phase, I worry about actual sound design and refine drum fills and add more parts. I think that enables you to not be tied to the choice of instruments you have available but you are able to hopefully create a solid composition before focusing on minor details.