I'm quite happy using words like old, obese, vaginally multiparous and so on if everyone could agree on definitions and use them consistently. On the other hand, "badsmelling folds of skin that wobbled, sweated and chafed at the smallest movement, aprons of fat hanging in front of their stomachs, batwing arms, thick flabby thighs and sagging breasts" is a realistic description of certain conditions (the quotation is taken from a published paper in medical health care philosophy.)
The reason why persons concerned are often offended by these terms is that their inner body image doesn't correspond with the outer physical fact. In day to day life, we try to focus on the inner person when we speak to someone (especially if they have their clothes on!)
For most people, sessioning with a prostitute is about the outer person, just as it would be if, for instance, you were joining a sports team. The phrase "a few extra pounds" (designed to appeal to the inner person and their ego) is less relevant than "overweight" (unless you are talking about sports like sumo wrestling.)
What term would a football coach use to players to players getting a fat salary and underperforming? I suspect it might well be something even more graphic than phrases used here.
Use of graphic language on UKP though has probably risen also as a backlash against fluffie reviews that identify with the prostitute's inner person to the point of being gratuitously misleading. No woman, no matter how fat or ugly, is ever fat or ugly in the fluffie's report. He sadly gives her 10/10 while mentioning that she was "a little heavier than I had anticipated" or says she is a "beautiful sexy lady" when he means her projected personality. Punters have got so fed up with seeing such rubbish every day on prossienet and adultwork that many want to have a forum for more discerning punters that the censored language of prossienet could never provide. By using more extreme language, they set their face against euphemistic descriptions.
All a bit academic if you like, but I'm aware that there are some intelligent-minded punters who question it and I think a serious response is not inappropriate. But the bottom line of course is, if it's not against the rules then it's the individual punter's choice
https://www.ukpunting.com/index.php?topic=31076.msg434212#msg434212