If the only concern was "water...now" you'd have thrown up any old ditch or piping and called it a day. Of course it would be long gone by now.

Numerous other examples exist. Bazalgette over-engineered his sewerage system in London such that large parts of it still function perfectly well today despite the growth of the city. Even having the foresight to include secondary tunnels for other infrastructure alongside the sewers. It's over 150 years old but was carefully thought out, properly built and designed to work beyond a tiny lifespan.

If people believe bitcoin is to be a system used well into the future, it makes sense to engineer it thoughtfully and robustly.