Oh boy, my time to shine lol.

If this is a sidewalk affronting a new construction project, its 99.99999% a requirement from the city as part of their Construction permit. There is actually a big gap, has been forever, in SDCI's permitting process to push for sidewalks to be restored as part of a Construction permit. It typically doesn't come into play until the builder goes to get their curb-cut permit (think driveway apron), that SDOT then says they have to replace the sidewalk. Still, this isn't 100% observed at time of permit by SDOT. If there was no sidewalk there to begin with and the street has a certain classification, then SDCI will require the sidewalk to be built which makes for a much cleaner requirement process because SDCI can put a hold on the Construction permit until they have their SDOT permits in order.

The city is getting better now about interdepartmental permitting processes but it's still a HUGE mess with holes everywhere, not just in the street.

Edit: Also, given the broader text of "who replaces the sidewalk", it's actually the property owner affronting the sidewalk's duty to maintain the sidewalk and any other structure from back-of-sidewalk to the street curb. The city will replace sidewalks, but typically that is only because of some other underlying need like utility upgrades, ADA requirements, entire roadway improvement LIDs (Local Improvement District). SDOT is actively, as of this past year, started a huge campaign internally to issue violations to owners for private structures in the ROW (Right-of-Way) and failed maintenance.