Wilson Combat 300 Hammer is now SAAMI accepted.

[Fess]

I think that it really comes down to fact that some people just have a fondness for a certain caliber. Those of us who grew up watching movies and TV shows about WII pretty much associated .30 cal with the United States and manly men, dangit. It took a long time for some of us to accept that something as small as 6.5mm could be a good all-around hunting cartridge.
For someone who is determined to have a light recoiling .30 caliber cartridge in a handy semi-auto package, the 300 Hammer is a pretty good choice. The 300 Blackout sacrificed a lot of its supersonic performance in order to accommodate long projectiles for subsonic use.