I disagree with losing weight being easy. It's easy in "theory," and if you only have 10-20lbs to lose it's pretty straightforward.
Enter human psychology, "real life" (stress, kids, a job, social life, etc), and the fact that maybe you have 80lbs to lose. That, at a healthy pace, can take a full year to lose. Or 80 weeks (nearly a year and a half) if you go one pound a week. That's a long time to stick to a "diet."
That's why most people need to focus on a lifestyle change. A Diet implies short term in most people's mind, and that's why most people revert. Yay, I lost 80lbs, now let's start eating donuts for breakfast, McDonalds for lunch, and pizza for dinner again. It's trivial to gain weight. It's harder, much harder, to lose it.
FWIW, I'm a weightlifter. I've been as much as 50lbs overweight, lost that weight and kept it off for many years. I've also gone through the bodybuilding "bulking/cutting" cycle that was popular for so long (and maybe still is, I don't do that anymore), so I'm quite familiar with gaining 20-30lbs and cutting down again in cycles. So I know weightloss is straightforward and simple, but I totally disagree that it's easy.
I have no idea why people are voting you down. It must be out of pure utter ignorance with no practical experience in trying to do this. As someone who weight lifts naturally what you said is factually correct viz. (a) it is as easy as counting calories and eating at a deficit. (b) it's difficult to eat at a deficit and keep muscle mass because you're essentially low on fuel and your body has to burn something for energy, trying to stay out of a catabolic state requires diligence.
I didn't down vote, but saying that losing weight is easy is like saying playing the piano is easy. In reality, they are indeed both easy, but you need determination and time.
Then the word easy is being used in two senses. Technically losing weight is extremely easy. It's a closed problem. It might be not-easy in a way that varies from individual to individual but to say that it's not-easy should be qualified in some sense to show that it's a psychological/will power/whatever problem and not because we have an incomplete understanding of nutrition.
I know people who were able to dunk in high school as teenagers and were very explosive. Than they started weight lifing regime, lifted hard for a decade (solid weights on compund movements), still can't really dunk no more, while they should be even more explosive.
Thing is, pylometrics is still nr. 1 for most explosivnes and also olimpic lifting, but not classis weight lifting, strength is not power.
+EDIT: This guy on the video does far more than just DL to achive what he does, he is also very competent at calisthenics, he does one leg hill jums and other extremely difficult exercises ... Claiming this is a product of solely DL is misinforming.
Americans seems pretty short nowadays compared to some countries in Europe, where average is near 5-11 and a few over 6'. Still a few short countries here in Europe too.
Keeping low body-fat % while maintaining decent amount of muscle is what is really challenging.