They weren't, though, not really. The tech industry just moves too fast for that kind of pronouncement. It's absolutely true that a Sun-3/75 in 1986 was a revelation[1], but every one of those features was cloned as free software and running on sub-$1000 hardware by 1994. They likewise had a brief moment with SPARC in the early 90's where their machines were the fastest you could buy, but Intel demolished those hopes too[4]. Their swan song was the early dot com boom, where they still held onto the reputation as "The Best Unix" and sold a ton of web server hardware to the more conservative outfits. But we could all see the writing on the wall even then.
I mean, it's true they had some great stuff toward the end. But not that great, and generally not marketed in a way that would help them. Containers are actually a good example. Solaris Zones were... just a weird circus act[2]. I don't know any major players who made bets on the technology. And, again, within 2-3 years Linux had cgroups and LXC running[3] in a more performant (and much cheaper to deploy) environment and that's what Docker picked.
[1] Faster than a VAX, which was still the reference Unix box. Megapixel framebuffer with windowing and competent terminal emulation. Every box was on the Internet. Every box could see the rest of its network over NFS (and most were deployed diskless). FWIW: anyone know where I can get one? Would love one for the collection, but most seem to have disappeared (government and university equipment tends not to end up on eBay...)
[2] Edit because this was misunderstood: I'm saying it was an oddity with minimal uptake, not that it was chaotic or bad as a matter of design.
[3] This too got misunderstood, though I don't see how. I'm really not interested in a flame war about whose container technology is better. I'm just saying that to Sun in the early/mid 00's, it wasn't much of a competetive advantage (as evidenced by the fact that it lost to Docker).
[4] Ooph, this one too. I'm saying that in the early 90's SPARC was dancing with MIPS for the fastest CPUs on the planet, but by the release of the P6 core that was over and Intel had essentially won (though DEC kept the dance going a while longer with Alpha). I'm just amazed at the propensity for folks here to jump in to argue stuff that in my mind was settled decades ago.