I believe those are temperatures in the actual tunnels, a passenger's experience in a crowded tube car will be quite a bit warmer!
Newer units on the subsurface lines do have AC fitted.
This offers 2 distinct improvements for passengers.
1. noise/dust mitigation: One can sweep the platform floors all you want, but dust from the track will always get to the platform. By installing the glass partitions, general atmosphere of the platform is just more pleasant.
2. less space for AC to cool: It's impossible to cool ALL of the space of a subway system, from miles of tracks to the platform. By installing the glass partitions between tracks and platforms, AC at the subway stations only has to cool the platform.
I heard NYC subway engineers say they can't install the glass partitions because the subways are not capable of stopping at a particular spot. This is required for the glass partitions to be installed.
Mines quite successfully manage to cool air 2+ miles under ground, so I'm finding it a rather hard to believe that nothing can be done about this.
The deeper tube cars running on older lines have serious space constraints to deal with that make integration of things like cooling equipment difficult and expensive. We're talking about trains that have comically small proportions relative to what you would see anywhere else in the world.
That said, last I had read, the deep line cars are supposed to get AC sometime within the next decade or so.
Don't think so. That is a fixable problem. (e.g. convert the space of 1 seat per car for an AC unit).
The fact that everyone is so stumped by the problem says it's the actual tunnels that are overheating. The fact that some lines don't have AC just exasperates this.