Samsung has made much ado of the Galaxy S20 Ultra's enormous camera array, but just what's in there that requires a conspicuous hump on the back of the phone? You don't have to wonder. iFixit has posted a teardown of the range-topping beast, and it's clear Samsung really didn't have much choice. The 108-megapixel primary camera by itself is huge -- the sensor covers twice the surface area of the 12-megapixel unit in the iPhone 11 series. The periscope-like zoom camera, meanwhile, needs a lot of space for its unusual lateral design, including optical image stabilization just for the prism.
The disassembly also shows just how little space there is for the actual chipsets once you rule out the cameras and the giant 5,000mAh battery. The spider-like circuit boards are stuffed to the gills with components, including the Snapdragon 865 processor and X55 5G modem. That might partly explain why there's no headphone jack, although that won't be much consolation to fans of wired audio.
You probably won't be fixing it yourself, at any rate. You'll have to unglue the rear cover just to poke inside, while the display and battery are particularly difficult to replace. Samsung built the S20 Ultra to make the most use of its cavernous dimensions, and repair definitely wasn't the highest priority.