Sure upgrading infrastructure is possible but the costs are huge. It's subject the same inflation as everything else, plus city worker unions have a lot of political power. Once a sewer line reaches capacity we can't do a minor increase; the whole thing has to be ripped out and replaced which is tremendously disruptive.

A real-world example to support your comment that my civil engineer buddy recently told me: in Columbus, one of the main streets past Ohio State University into downtown is completely at sewage/rain water capacity. Decades ago when the street in question (High St) was being built, the only buildinga along it were single/multi-family homes. Now there are large student dorms and apartment complexes. During intense thunderstorms, the gutters along the street which feed the sewage system reach capacity and the whole street floods. And I mean floods.

This is an "easy" fix in theory: gut the previous system and just build anew. The problem is, that would be such an enormous undertaking (b/c you have to divert sewage during the whole process, etc) that the city is effectively forced to apply what amounts to band-aid fixes in its place.