Having lived in SF I've seen many cycles where the SFMTA says "We'd like to make (insert any changes)..." and the 'advocates' immediately come out of the woodwork to make the argument you're making, about how walking another block or two is impossible for some constituents.

Fundamentally as another commenter here said, a bus "can't wear two hats." In most large US cities, the bus, and sometimes the subway (if one exists), is mostly a welfare program, and its target demographic is the elderly, the poor, and the homeless. Two of those groups are rarely in any hurry.

The fact that urban professionals also rely on transit to actually get to work is not very much considered in the decisions ultimately made. This is why any changes to it are so fraught.

To actually serve both populations, you'd need to have two independent systems, but that would represent a tremendous amount of incremental cost. That's why they used to have (do they still? I'd guess not, post-pandemic) buses paid for by Apple, Google, Facebook etc. to shuttle people to work -- it's something the city government could never accomplish because the choices that make transit useful to those with jobs make it problematic for the other group.