I believe HQ staff was very unhappy about that situation and that (some of?) the warehouses in hotter places have A/C now. (Source: live in Seattle, know a number of Amzn employees.)

I haven't seen any articles about the working conditions at warehouses in years, have you? In the mean time, they've opened dozens more warehouses.

(The latest was the NYT article which was about office jobs and which is a whole discussion in its own right.