Typically it’s cheaper to maintain vs wait for stuff to fail.

My wife used to be a finance director for a water utility. Part of that gig was having a capital program that proactively maintained infrastructure.

When they started that program ~20 years ago, they were criticized for a resulting higher rate structure. (5-7%) more than a similar city in the region. But now… that difference flipped and then some. A key failure of critical valves in the neighboring city cost nearly $10M, while the planned replacement was like 80% less.

I have experience as a reliability engineer in infrastructure. I would say it's very context dependent, but for the most part it's cheaper to maintain up to a point. A lot of the contextual distinction comes with the criticality of the component. Critical components, by the definition of being critical, have a high downside of failure (whether that's cost of operational). I will say that there are some occasions where it may be cheaper (both in financial cost and availability) to run something to failure.

The real problem IMO is that cognitive biases can prevent people from making those objective decisions. When dealing with things like probability of failure where there's uncertainty, it's easy to be swayed by a competing priority that feels like it has more immediacy and less uncertainty.