Well, the main thing is that beaker count is the base value used for calculating the weight. Added with the fact that the turn counter weight increases linearly, we can see that early game tech trades give much less WE hate than late game since tech costs increase much faster than linearly. Consider:
Turn 100 Priesthood trade ~ 60 / 100 base values
Turn 300 Assembly line trade ~ 5000 / 300 base values
Turn 100 Priesthood trade ~ 60 / 100 base values
Turn 300 Assembly line trade ~ 5000 / 300 base values