Each era builds its water, sewer and trash systems around its current explanation of what makes people sick. Bad-air theories, then germ theory, then ecology each produced different priorities. Systems built for one theory are poorly suited to the problems the next one reveals.
Public outcry can spark cleanup drives, such as citizen-led clean-city campaigns against dumping and contaminated food. Without lasting civic institutions to carry the work, the gains don't stick.
Bringing a public water main to the street is a long way from taps, toilets and tubs inside homes. The last stretch depends on property owners paying for it. Where owners rent to the poor, a generation or more can pass before tenants get plumbing.
Cities build water supply first because it is the central service. Sewers and garbage removal arrive much later, even when the need is long recognized. The incoming service sets the pattern that the outgoing ones must later fit into.
When cities lack proper disposal, every kind of refuse gets mixed together and dumped on vacant land, and in practice that means in poorer neighborhoods. Those neighborhoods protest, but they carry the burden first.