Getting to around 10% isn't that hard, I went from about 18% to about 10% in a few months. All I did was lift heavy and eat clean. My diet consists of mostly lean protein (including a ton of fish, I eat about 4lbs of salmon a week), eggs, vegetables, nuts and the occasional fruit. I sprinkle in cheat meals from time to time, and I usually try to have my cheat meals either immediately before or after a workout. I find it easier to just eat clean and eat when I'm hungry and not worry about counting cals
It may be easy for you to get that lean, but, for most, it's a long, painful process that requires a lot of micromanagement and produces an utter disdain for food. Many men start to have trouble when dieting below the 12-15% mark. Most peoples' hormones become out-of-whack; leptin sinks, grehlin starts to rise, T levels drop, cortisol is dramatically elevated, etc. I've personally seen quite a few formerly obese people get to this point and
give up on dieting altogether after years of steady progress because it gets so hard psychologically.
Like S-D said: for most people, getting to sub-10% gradually is very difficult.
I'd also like to note, as an aside, that being below 10% isn't always optimal for fighting. The point of diminishing returns with respect to performance is reached rather quickly once you drop past that point. I thought getting down to 8% from 9% would make me a better, quicker wrestler. I spent about a month agonizing over it, only to realize that, once I reached 8%, I was no better at wrestling than I was at 9%, or maybe even 12%. I did, however, manage to drop into a different weight class where I was very strong. I'm currently trying to push this as far as I can while recovering from an ACL tear.
Not everyone can walk around at 7.7% body fat like GSP and still be a monster, and get into the mid-high 6% range on fight night while maintaining their functionality. The only people who can do that are either extremely, extremely genetically-gifted, extremely genetically-gifted people on good drugs, or genetically-gifted people on the best drugs money can buy.
(Also as an off-topic aside): I also have a problem with dudes thinking that they need to be sub-10% in order for women to like their bodies. Women generally think 12-15% looks good. Let's be real here: the difference between 12% and 10% is so minute that it almost doesn't matter. An average, well-built guy who is 15% can flex and still get 2-4 abs showing, too, thus making the gap between 12% and 15% look relatively small. It's sort-of like how we look at women and see that some are clearly fit and look good, and slight variations in body fat either way don't really make a huge difference.