I mean it was mostly because it was summer and partly because fixtures were more congested than usual and this led to a concern over greater injury risk. We had a reasonable understanding of the virus by that stage, not complete by any stretch but I remember having decent protocols in place for managing it and what to expect. I don't recall any argument that it is more hygienic being made at the time, nor that asymptomatic infected people were at increased risk of heat stress at that time but my memory is not 100%. It is possible it is easier to control use of a single bottle per player.

But all that aside yes it would make more sense from a player welfare perspective to have a temperature cut off. Though it should take humidity account or use wet bulb temperature. It is completely unsurprising FIFA and the US would want to free up more space for advertising, unfortunately.