Many large buildings maintain full-time maintenance people on a salary basis. For your smaller general office parks these are usually generalists, but for your larger skyscrapers, data-centers, etc you absolutely can and do see electricians, plumbers, etc working on a regular salary. No they do not bill per-repair in this situation.
That's a team of cheap slackers who do just enough to keep the water running. It's against their interests to find more work for themselves. You may try to force them by adding personal liability for failures they neglected to prevent, but that's going to have the opposite effect: now only cheap and dumb slackers would sign up. The contract we're discussing is like the impossible ladder: it has many cool properties, but it can't exist in reality.
That flies in the face of my direct experience working with these people, but sure let's take your assumption at face value.
By this logic everyone on salary in any career must be a cheap, dumb slacker, after all there is no difference between accounting on salary, plumbing on salary, writing software on salary or working in a warehouse on salary. The exact same logic applies.
Or maybe, just maybe doing plumbing on salary has the exact same set of tradeoffs as doing any other job on salary and people choose either for different reasons.
