I work in a 10-story building built in the 1890s, one of the first "skyscrapers" in San Francisco. The mail chute system is blocked, and the beautiful iron staircases have been boxed in at every level with fire resistant doors and walls. AFAIU, in both cases one of the primary reasons was fire safety, according to the leasing agent.
However, I know of at least one other building in this area, the Hobart Building, slightly younger but much taller, where the iron staircases are still open and still serve their aesthetic function. It makes taking the stairs so much more pleasant.
Apparently the fire risk is manageable. I think a bigger problem is that these building were designed for a multitude of small office suites. But today most of these buildings will have (or want to have) tenants who wish to lease entire floors, or most of a floor. Large, open, but single tenant floor spaces are how most modern office towers are constructed, so that's the market expectation.[1] It's difficult to provide such tenant spaces while also keeping open corridors between floors. Even for mail chutes, as the private, controlled-access floors diminish the desirability and utility of shared facilities.
It's interesting it peaked in 2001 concidering a large part of NJ's mail system was essentially shut down for a few weeks. Not that NJ is that big, but it's big enough that I'd expect it to cause a 1-2% hit overall.
However, I know of at least one other building in this area, the Hobart Building, slightly younger but much taller, where the iron staircases are still open and still serve their aesthetic function. It makes taking the stairs so much more pleasant.
Apparently the fire risk is manageable. I think a bigger problem is that these building were designed for a multitude of small office suites. But today most of these buildings will have (or want to have) tenants who wish to lease entire floors, or most of a floor. Large, open, but single tenant floor spaces are how most modern office towers are constructed, so that's the market expectation.[1] It's difficult to provide such tenant spaces while also keeping open corridors between floors. Even for mail chutes, as the private, controlled-access floors diminish the desirability and utility of shared facilities.
[1] The nearby Crown Zellerbach Building (1959, https://en.wikipedia.org/wiki/One_Bush_Plaza) was at the vanguard of this office tower design evolution.