follow the money.......
I have asked myself same question for years, as I have been reloading for 7 Rem Mag for almost 40 years. I hate to sound like a conspiracy buff, but my take on your question is that it is hard for manufacturers to sell new guns because the old ones don't wear out. So they need to create a need. In the case of 7mm cartridges, they created a need by castrating the 7mm rem mag with mild factory loads. That clears the way for all those new short/fat/long/big wonder magnums. The only place I know to get good data for the 7 Rem Mag is the Nosler Reloading Manual. They have a load for 3200 fps with a 150 grain bullet. If you can't do it with that one, you need a bigger caliber.