First were the big mergers like the ones between American and US Air, and between United and Continental. They reduced competition, which is something Buffett hated.
Second, last year was a brutal year for airlines and many new planes were added. Airlines are now cutting back on expansion plans for 2017.
The lack of new capacity is critical to pricing in the future, and it could lead to up earnings years. Hence, Cramer found it absolutely crazy that major airline stocks are valued on an average of just eight times next year's earnings estimates.
Third, there is a scarcity of narrow body planes, which are the ones that make the airlines the most money. So even if they wanted to increase capacity, it won't be easy for them to do so.
Fourth, fuel is a huge variable, as jet fuel often takes up 25 percent of costs. With lower oil prices, the fuel issue seems under control.
"Perhaps Buffett feels we are in an era of permanently lower oil prices, although, oddly, higher oil prices have often led to higher stock prices for the airlines as higher oil prices signal further gains in economic activity," Cramer said.
Lastly, it could have been a bet that worldwide travel growth will resume.
So, with price wars subsiding and companies making more money, a lot has changed since Buffett last invested in the airlines.
"They have become quintessential Warren Buffett stakes with only one caveat — they were a heck of a lot lower when he started accumulating them, so I would wait for a pullback because today's Buffett induced rally might not last, and lower prices could be beckoning," Cramer said.