In my experience, KISS results in the easiest solution to maintain. Then I get a litany of complaints from devs that "this isn't programming" or "this is a dead end to my career" and then they leave. Which paradoxically makes it more difficult to maintain, as I have no maintainers lol.
Not saying that latter is the case here, but I've ran into devs maintaining some monstrosity and then complaining about others pushing for off-the-shelf solutions not realizing that nobody wants to spend time learning some bespoke system they created that's not actually as great as they think it is.
Not going to bash younger devs in general but the fact is that getting the job done without thinking of their future career... is usually not high in their list of priorities.