Marketing/greed in guns & ammo...which is pretty much what is needed to have a company survive the competition...is by far the biggest reason. However, I think a minor factor would be the better communication and travel since the early 1900's. What I mean is, there are european work-horses (6.5 Swede) and american work-horses (30-06). Anytime you increase the interaction between two pools of products you'll start to see a blending. Example the 7mm-08. Also, better manufacturing methods have made higher chamber pressures safer...which I think may be to blame for the magnumitis. That, and human nature: "oohh, its bigger? It's faster? WELL it MUST be BETTER!!!"