You'd have a better bridge, at the expense of other things, like hospitals or roads. If people choose good-enough bridges, that shows there is something else they value more.
Don't we end up just spending the same? Just now we're left with a crappy bridge.
Obviously, there's a way to do both poorly too. We can make expensive things that don't last. I think a large chunk of gripes about things that don't last are really about (1) not getting the upside of the tradeoff, cheaper (in both senses) more flexible solutions, and (2) just getting bad quality period.
On whole it is entirely reasonable optimisation problem. What is the best lifespan of single bridge over desired total lifespan.
We only recently figured out how to reproduce Roman concrete.
We’d have more but a lot were blown up during WWII.
The difference is that they didn't have rebar. And so they built gravity stable structures. Heavy and costly as fuck.
A modern steel and concrete structure is much lighter and much cheaper to produce.
It does mean a nodern structure doesn't last as long but also the roman stuff we see is what survived the test of time, not what crumbled.
Roman concrete is special because it is much more self-healing than modern concrete, and thus more durable.
However, that comes at the cost of being much less strong, set much slower and require rare ingredients. Roman concrete also doesn’t play nice with steel reinforcement.
Modern concrete is more uniform in mix, and thus it doesn't leave uncured portions.