There is much more to software than web apps\cloud apps. There are types of software apps where continuous delivery may not be possible since not every software follows a push model . Operating systems\ compilers\ Library frameworks\ Native apps where the customers have a choice of not installing the latest version of the software released by the vendor, systems like those that run in the cars\ mobile phones \ ATMs\ enterprise devices and other offline machines. Production endpoints in such places are not controlled by the software vendor and knowing and controlling the exact version is critical in terms of providing patch versions for things like LTSR releases and legal compliances and ...hence the : gatekeepers.