When/how/why max tire pressures raised from 35 PSI to 44 PSI?

P metric sizes are "usually" a max of 35. Pressure varies with what load range the tire is. I have load range E on my truck. Their maximum pressure is 80 PSI. I run them at 60, because 80 would beat me to death in that old truck. That said, I have done both long term. Used the vehicle recommendations and used the max tire pressure for the given weight rating. I have found that the max pressure gives the most tread life. I will gladly give up a little ride quality for a tire that lasts longer.