Sanitization. Your dishwasher spreads dirt and bacteria around and tries to remove as much as possible with a clean water rinse. Bacteria get into every micro-pore and nano-sized crack, where detergent is unlikely to penetrate effectively. Heat doesn't discriminate (unless we're talking prions, but I digress) and will kill everything that remains.
I can't see how that's true. A quick search tells me that dishwashers can get up to a max of around 60c, that's nowhere enough to kill most bacteria, especially ones hiding deep inside cavities. Maybe you could pasteurize milk in an extra-long run of your hot cycle, but it won't come close to sterilizing stuff.
Fair enough, but let's say the goal isn't to kill everything, but common bacteria that causes problems, such as salmonella and e coli. 60c is enough to handle that.
It's non-issue in any case. Quite a few people on the planet really need to sterilize their plates, spoons, and forks just to have a lunch. And with rare exceptions 60°C + soap is more then enough for all that stuff to be safe.
I haven’t seen any quality evidence that dishwasher dry cycles effectively “sanitize” anything. Really not trying to be a “but actually” dick, but without this information it’s just marketing mumbo jumbo.
Here [1] is a reference of a citizen experiment to test the sanitize cycles. There are also experiments regarding clothes and apples that are quite interesting on this website.
