Most load data DOES come from manufacturers because most ammo shot is factory loads. Non-handloaders far outnumber handloaders. For them the load data is limited to external ballistics, but that is OK because the loads are pressure tested by the manufacturers and pretty much all the shooters are interested in is the external ballistics and bullet construction.
If your beef is with .308 factory loads, then we're actually in agreement about that. Most factory .308 is download WAY below SAAMI and/or with overly fast powders to avoid bending crappy cast M1A op rods.
Of course if your constrain .30-06 to only factory ammo that will run in a Garand, it doesn't look so hot either.
