I don't see how this would work because you're saying that the older sidewalks are scrapped and rebuilt when they hit a state of 'x' deterioration, so you only see > 'x' state ones. But how then could it be that newer sidewalks are allowed to fall below 'x' instead of also just being scrapped and rebuilt?
Politics, money allocation, taxation, etc. The US had a golden age last century and is now in decline. It can still bounce back but it needs a political and legal revolution, in this particular case, it needs to tax the wealthy and spend it on municipal improvements.
But that's socialism / liberalism and apparently that's terrorism now.
Municipal budgets cratered hard over the past couple decades, roadway maintenance is given precedence over sidewalk maintenance, and SUVs and electric vehicles do considerably more roadway damage per vehicle. So there’s concurrent causes promoting a global decay in sidewalk maintenance in cities that expanded without the necessary tax base to support maintenance: see for example Los Angeles (current-day example!) repaving all but one foot’s width of their roadways so that they don’t have to fix broken sidewalks. This doesn’t contradict the survivor bias point! If anything, it’ll accelerate it: you’re about to see just how many (or few) sidewalk squares survive the underspend. Citizen science, here we come!