Singapore marks a key point in the Formula 1 calendar. With the low-drag races out of the way, and now beginning the end-of-season flyaway leg of the championship, the remaining races are at medium-high downforce tracks, and from now on the cars do not return to the factories.
So Marina Bay is a key place to try new parts in anticipation of the upcoming races. Nearly every team has updates for this weekend. Some parts seen in free practice may not be raced, but will re-appear at the subsequent races on permanent tracks.
This street race is obviously a high downforce track, with a strong emphasis on brakes. It's not that the brakes are worked especially hard in comparison to other tracks, but repeated use, without long straights or a cool climate, increases the pressure from overheating.