300 Yards a long hard to make shot???

I am new to hunting, and by new I mean I have never been on a hunt and I do not know any hunters, I have just started watching hunting shows and videos online. I was a sniper in the Army, and the Army was the first time I had ever handled any type of wepon, so it is all I know when it comes to shooting. That said on most of the shows I have seen about hunting the guys say stuff like " I would like to get closer than this" or " this is going to be hard at 300 yards". Now as a marksman in the Army those were super easy shots for us< is there someting I am missing here? Is it just the caliber of ammo being used? I used what amounts to the .223 and the 308 most of the time. Any info would be appreciated?