None of these are why. Linux succeeded because the incumbents were so intent on fighting Windows NT without making real changes that they created a terrible sit

None of these are why. Linux succeeded because the incumbents were so intent on fighting Windows NT without making real changes that they created a terrible situation for developers and operational staff. Entire companies existed to make multi-vendor Unix frameworks and the vendors themselves weren't in great shape by the late-mid-90s. Given the choice between standards and varying compliance (and there were a plenty of these and so #ifdef IRIX... never went away) and just picking one sub-optimal solution that was available on commodity hardware, the outcome was obvious. The same situation is playing out in other industries as well right now.