I've in this area professionally for some time now, and I've never "maintained" servers in any reasonable sense. There are kernel people who maintain the kernel and there are Debian devs who maintain the operating system. The server may be mine (but more often that not, it isn't) but only in very specific circumstances do I ever concern myself with maintaining any part of this stack.
A vanilla Linux VM is a platform to build on. Just like AWS or anything else. It is the environment in which my software runs.
Thus far, something like Debian has been more stable and much less of a moving target than any proprietary platform has been, cloud or non-cloud. Should a client wish to minimize maintenance costs of the software over the coming decade, it is most cost effective to not depend on specialized, proprietary, platform components.
That may change in the future, but right now there is no indication that is the case.