308 has been worked on to death by the military of many countries so there is a ton of info about what works and what doesn't.
270s can be decent shooters to be sure, but typically they shoot 150 gr and lower best, the 308s typically shoot 165 to 175 best. The fact that lighter bullets tend to be affected by wind more than heavy bullets do is 1 reason, also heavier bullets maintain supersonic speed longer (further down range)
308 also has light recoil and is a very efficient cartridge as less powder is used. The other real advantage any 30 caliber catridge enjoys is the sheer volume of bullet availability, from 110 gr to 295gr round nose to vld and ulds.
This just is not the case with many other calibers.
Another reason so many use 308 is there are a great number of precision type rifle offered in that caliber as a factory offering.
There is absolutely no reason that a 270 could not be made into a precision rifle, and with some custom bullets I would think 1 could do very well. The US shooting fraternity pretty much dictates what the world shoots, not that long ago 6.5 was a scoffed at caliber, a .264 dia bullet that weighs 140 grains was considered far too light to be useful, until some of the guys shooting 6.5x55 and then 6.5x284 started kicking ass at alot of the 1000 yard shoots in the US, now it is a very hot cartridge to use, but has taken time to gain acceptance with the BIG shots down south.
I was laughed at 25 years ago ,when I built a 7 Rem Mag F class rifle, until the results were posted. I found the same thing higher bc bullets, then built the rifle around the cartridge, and it worked very well.
