It's not the case because temperatures are correlated; If <random suburb of $BIG_CITY> sets a high, it's likely that $BIG_CITY will as well.
However, we should be somewhat regularly setting new highs just because we have on the order of just 200 years of data (so just 200 data points for each daily high); if the planet were not warming, and the high for any given day will be normally distributed around some average for that day, then as time marches on the odds of getting an extreme outlier increases. Some cities on some days will have a high that is very improbable, while others will not have gotten "lucky" yet.
However, we should be somewhat regularly setting new highs just because we have on the order of just 200 years of data (so just 200 data points for each daily high); if the planet were not warming, and the high for any given day will be normally distributed around some average for that day, then as time marches on the odds of getting an extreme outlier increases. Some cities on some days will have a high that is very improbable, while others will not have gotten "lucky" yet.