I think; There could be other factors, but this is the main one
I'd guess that, on average, the bulk weight of the press loosely determines its maximum pressure... Just because it needs a certain amount of steel to confine and direct that pressure without damaging itself.
Over time, the engineering gets tighter and with less excess. You know that phrase, "anyone can make a bridge that stands up, but you need and engineer to make a bridge that just barely stands up"
It probably becomes an economic issue, especially given the bigger your press is, the less people are going to need it for something.
I'd guess that, on average, the bulk weight of the press loosely determines its maximum pressure... Just because it needs a certain amount of steel to confine and direct that pressure without damaging itself.
Over time, the engineering gets tighter and with less excess. You know that phrase, "anyone can make a bridge that stands up, but you need and engineer to make a bridge that just barely stands up" It probably becomes an economic issue, especially given the bigger your press is, the less people are going to need it for something.