Those kinds of products are huge investments. Sure Apple might be able to market towards the enterprise, but they simply don't think there is any money to be made. They used to have for instance Xserve that tried to stay afloat in that market, but which made little money. Since they canceled it, Mac OS has only been developed as a small to medium server (which it isn't half bad at). But big time data centers are a different world.
For instance, as a very basic example, does Mac OS support Infiniband or the more exotic high-speed ethernet network interfaces? For Infiniband, the answer is no and in the other case the answer is "kinda, but not really."
In the pipeline:Migrating to the new shiny Mac Pros along with OS X Server
Reasons: Thunderbolt 2 connectivity is amazing and works fine to connect FibreChannel RAIDs. OS X Server: Though it's correct that the GUI got simplified a bit, it's the same server package and complex as it always has been, however easy enough to support. And if configured correctly, a solid workhorse for many scenarios: network accounts for lab use, calendar and contacts server, along with some helper tools it works in heterogene environments fine, supports huge amounts of users in via LDAP..just to name some reasons. for 20 bucks the best server os to support Mac and iOS clients. And because the underlying foundation is UNIX, it's friendly with any networking stuff such as RADIUS for your WP2-Enterprise wi-fi needs..just to name a view.
One thing that is not quite right in the post above: SAN support exists via XSAN.
Red Hat/Suse/Oracle etc. all sell tailored solutions for that usage that are Linux specific technology (mostly, some stuff gets ported to other Unix derivatives but most doesn't). Sure Apple could do all that too, but they don't want to. It isn't their market, so why sink money and effort into engineering OS X to do it when they can just buy high quality products ready to go?