a.k.a. stagnation?

No, the ability for the machine to not crash or need to be rebooted for long periods of time. Linux has gone completely downhill in this respect for the past few years. Switching to Solaris on my main Unix workstation has been a breath of fresh air compared to the constant naggering from Linux systems for updates, but I like old school...because it seems to 'just work'.

Many Linux systems now support livepatch to update the kernel for security fixes without rebooting.

ZFS storage layers built on OmniOS/OpenSolaris/Illumos enjoy more years of maturity (and thus demonstrated stability) than upcoming versions for Linux/Ubuntu. If you have to build large storage in-house, stability is a high priority.