I disagree. First of all, a trained craftsment for sanitary and heating installations has to think about stuff like where to put pipes, which angles to observe, which diameters are necessary… All of this does not matter for fixing an existing installation.

And second, when people learn the basic principles of it, they also learn how to better maintain things so they need less fixing in the first place. Also if there is no profit incentive, there is no incentive to provide overengineered but easily breaking systems but rather straightforward and reliable ones. For instance the hardest part of fixing my washing machine by myself was finding what the god damn error code meant.