Sun and SGI had a significant head start over NeXT. By the time NeXT shipped hardware, they were moving off 68k onto SPARC and MIPS respectively, building on successful and established product lines with the kind of hardware differentiation that NeXT didn't have the capital for. That's why NeXT had to change direction and make software such a major part of their strategy; they couldn't just re-play the same strategies that Sun and SGI got off the ground with, because those niches were now pretty well occupied.