Water and sewage have changed a lot over the years. Sure, you maybe can ignore it, but most cities regularly have to expand capacity and change technologies.
The type of waste going down the toilet has changed tremendously during the 20th century. As a couple of examples, pharmaceuticals and tampons frequently go down the toilet now (even if people are told not to flush them).
Additionally, acceptance of dumping raw sewage or overflows into waterways has hugely changed. I know many people who would roll up their windows when driving over the Potomac in DC. In Boston, the Harbor was absolutely atrocious and smelled for decades.
Together, these two factors have led to large amounts of research into sewage treatment, new technologies, and upgrades nationwide. Just because you apparently are ignorant of them doesn't mean they haven't been occurring.
The pace over the last 15 years has probably been slower, but if you look at the 1970's and 1980's following the passage of the Clean Water Act, upgrades of these systems were occurring on as large a scale as ISP upgrades. In fact, they probably were larger in total cost.