[qubex]

Two things come to mind: poor backwards compatibility and reliance on compilers to emit optimally ordered code (inherent in the VLSI system philosophy), which they proved unable to achieve, resulting in comparatively poor price/performance. Eventually x86_64 came along and provided an alternative that provided backwards compatibility, horizontal (PC/server) universality, and most of the purported benefits without the hassle, and the Itanium came to grief.

[CyberFonic]

The C compiler on HP-UX was an extra cost item and it wasn't cheap. Porting programs to HP-UX often required some tricky changes because the C compiler wasn't as mature as GCC on x-64 systems of the time.

I recall that once Oracle acquired Sun, they gave priority to getting latest releases of Oracle RDBMS and JVM running on Sparc before HP-UX and AIX. In the corporate space Oracle and JVM were pretty much the main game.