That kind of looks like what happens to me as I get down into the mid/lower 180's lb range. At 5'-11" (age 56) breaking into the 170's is damn near impossible. I kind of think something has shifted in my body, because at age 52, I was in the upper 170's and felt very little difference from how I felt in my 30's even though I weighed about ten lbs less back then, which is saying something because I was able to run a sub 5:00 minute mile in my 30's.
A couple of years ago, I had gained some weight up to 200 lbs and I set out to lose weight by at what I thought would be a modest 2lbs per week goal. I gave up alcohol, dedicated each day to walk an hour, and try to stick to one meal a day (a big salad) during the week. Weekends I was free to eat sensibly. To my surprise, my weight came off in a linear fashion to the tune of 4lbs/week until I got down to 184, at which point it predictably slowed. At that point, being more than happy with things, my plan was to slow things down and get into the 170's with a less drastic approach, but that never materialized and i eventually gained the weight back.
Even though I know, eating is probably about 80% of losing weight, I think once a man gets under 20% body fat, that we need some kind of movement related motivational factor to keep things going. That could be a race you want to do in a few month's, or a ski trip to get ready for, or some activity that you just want to get better at like cycling, or rock climbing, surfing, skiing etc. However, as I have gotten older, doing those fun things has become more difficult. There is a stiffness and struggle component there that was not there when I was just a few years younger. Joints hurt more, mobility is less, minor injuries occur all the time from seemingly out of nowhere caused by the most minor and random of movements. What was fairly easy to do just a few years prior has become something like pushing a rock up a hill.
It has been a major adjustment for me not having that extra motivational factor out there and within just a few month's reach. I still think I can get there, but I have really had to slow my roll and adjust my timelines, which does not always work as your graph has pointed out.