Basically, maintenance of complex systems or assets, are intellectually demanding tasks. All your examples, however, are completely the opposite. I am not saying that the jobs do not require skills, it's just that these skills are not that valuable.
Also maintainer adds value in the positive way. Where all your example is to prevent value loss. The 2 are fundamentally different.
Contrary to common knowledge, maintainer is not needed to make the system running, if nothing changes. Maintainer is necessary to make the system running in changing environment. Real-world software or any valuable assets require change to keep up with the world surrounding it. A great mental bias is to implicitly think maintenance is about "keep it running", where at the same time conveniently omit the part about changing environment.