[anthomtb]

I'm no expert but sewage seems rather simple in a tall building. You have gravity on your side so you "just" need longer pipes.

Its getting the fresh water up that should get exponentially more difficult as building height increases.

[sidewndr46]

Try dropping a baseball from the 75th floor of a building and watch how hard it hits the ground. You can't just have a sewage vertical going up that high.

[TheCoelacanth]

Sewage is far more difficult to handle than water.

You need to maintain a continuous downward slope. You are very limited in how you can have bends in pipes or two pipes join each other. You need to make sure air can get in and out of every point of the pipes, otherwise differences in air pressure will make things get stuck inside.

With pressurized water it just gets pushed wherever you route the pipes and you don't need to worry about the exact route nearly as much. Yeah, you need pumps to get the appropriate pressure on higher floors, but it's still simpler than sewage.

[unavoidable]

It's not quite that simple. If you've ever lived in a tall building and heard/seen/smelled stories of sewer pipes backing up, well you'll know what I mean. The bottom floor of a 50 storey building needs much more sewage space than the bottom floor of a 5 storey building. Anyway, there are considerations about venting, as well as increased capacity for lower floors versus higher floors, and the whole thing has to be designed in conjunction with the rest of the plumbing anyway.