I worked on healthcare.gov last year and it's hard to overstate the potential impact of a tool like DCOS. At one point, we had 2000+ VMs, most manually configured, with no monitoring, and completely different configs between dev, test, and prod (not intentionally). Straightforward operations like migrating half of the database servers from one VLAN to the other took months, small mistakes like changing a database password could result in hours-long outages, and simply getting the data that Mesosphere displays automatically would sometimes take weeks and other times simply be impossible.
Of course, clean devops hygiene would have eliminated much of the pain in the first place, but not every organization has the expertise to do things right. In fact, most don't, and the solution for most organizations is good tooling that automates as much of the system as possible and provides good development discipline for the rest.