Jean Bozman, research vice president at IDC Enterprise Server Group, said that the decline was due to platform migration issues, competition from Linux and Microsoft have not helped either. Part of the reason is the development of more efficient hardware with powerful processor cores, which are less expensive and requires less maintenance than Unix boxes.
It all started when people started to move away from RISC platform to x86-processor based alternatives. This could run many Unix workloads better. Meanwhile x86 technology also took over the new cloud computing and fabric-based computing. It looks like Unix will be around for a while, particularly in mission-critical environments, but many more will seek to divest their reliance on the platform, due to recent ecosystem changes or in line with IT modernisation, migration, or consolidation strategies.
At the moment the biggest maker of Unix boxes is IBM which took advantage of the turmoil at HP which was one of the biggest Unix box makers. HP-UX lost considerable market share to IBM. Oracle has continued to see declining hardware revenues too.