Elephant Walks aren't exactly new, they date back to WW2 when the numbered Air Forces in Europe would often generate in excess of 1,000 airplanes for mission over the European theater of operations. By the observers of these Air Force elephant walks it was often referred to as that because of the nose-to-tail taxi formations of the bombers; often resembling the nose-to-tail lines that elephants would walk in to move to the next watering hole. During World War II each combat group had four squadrons of aircraft to draw from to meet the mission requirements. Throughout the European theater elephant walks were daily occurrences that not only generated airplanes, but also constantly tested the capabilities of the ground crews, supply systems, and other support organizations.
In the SAC days, the term for the exercise was was "maximum sortie generation” (or surging). They were used as a tool by inspector general inspections (IG inspections) to test the capabilities of a wings levels of operations and mission readiness. An elephant walk, when used in IG inspection were sometimes limited to “taxi only” exercises and usually didn’t involve any airplanes taking off. In the 1980’s as many as 120 F-111’s took to the skies in part of a United States Air Forces in Europe surge operation exercise.
After the combat operations in Operation Desert Storm had ended, the 23/354 TFW celebrated the end of combat with an elephant walk of 144 A-10’s.
Their modern origins are somewhat grim. They became common in South Korea as a capabilities display and contribute to the readiness of American and allied squadrons in South Korea and nearby countries. In the event of war with North Korea, the plan is to quickly target the roughly 13,000 artillery pieces that Pyongyang has massed along the Korean demilitarized zone. In the early hours of a war, that artillery likely would bombard Seoul, which lies just 25 miles south of the DMZ. That's a serious, credible threat to the 25 million Koreas and approximately 150,000 U.S. citizens living in the greater Seoul metropolitan area. The US maintains three F-16 squadrons and an A-10 squadron in South Korea and two F-15 squadrons in Japan. Additional squadrons, almost certainly including F-22 and F-35 units, would join them during a crisis. An air campaign targeting North Korea would require 2,000 sorties per day.
By comparison, the allied air war over Iraq and Kuwait in January 1991 averaged 1,200 strike sorties per day and the U.S.-led campaign against Islamic State in Iraq and Syria averaged just 15 strikes per day. The roughly 100 U.S. F-16s and A-10s in South Korea and Japan — and any F-22s and F-35s that deployed in time for the first day of fighting — likely would be the first to hit North Korean artillery. And they’d have to launch fast to save lives in Seoul. So it’s not for no reason that the 7th Air Force in South Korea and Japan has organized more elephant walks than most Air Force commands have done.
The 7th Air Force has conducted most of its mass-takeoffs, which require intensive planning and maintenance efforts, under the auspices of the annual Vigilante Ace exercise. This is why so many elephant walk photos are of Vipers and Hogs.
Those Raptors in OP's post are PACAF jets from JBER. They'd be a part of any campaign against North Korea, so it would make sense for them to participate in such readiness exercise, even if they're still at home. F-35s at Hill have started doing them as well.