Because extended sessions out in the surf can leave your lower half looking like it got in a slap boxing fight with someone who is really good at slap boxing, and rash guards seem to guard everything but your private stash, SD-based Elephant Surf spent almost two years in R&D attempting to fill a gaping hole in the industry, finally creating "the Ultimate Surfing Compression Short", which they've dubbed "The Trunks", presumably because you can safely keep your junk in them.
So good that high-flying Aussie Josh Kerr feels totally normal being sponsored by tight small shorts, the trunks are mostly constructed of quick-drying, four-way-stretch, Spandex-esque material with textured 2mm neoprene panels (or "Elephant Skin") on the inner thigh/ behind the knee to protect the most commonly chaffed areas, while preventing awkward slippage so you're not "constantly adjusting", since you did enough of that when your mom married Rick. And since leg muscles are pretty damn important for shredding, the "under-board-short wear" operates by the same principles as out-of-water athletic base layers by compressing leg muscles and tendons to keep the blood flowing (i.e. keeping them warm), prevent strains/ tears, and stave off fatigue allowing you to stay out in the surf
just sitting on your board and telling everyone you'll get the next one longer.
In case you also like wearing clothes that aren't super-tight and short, they're rocking apparel ranging from thin v-neck sweatshirts to a tee with the words "REPRESENT SD" on the front in red, something you'll be much more confident doing if your backside isn't that same color.