Poachers just take the horn and leave the rhino to die. The reason poaching has gone down is that the main nations in which the rhino horn is smuggled to (China, Vietnam) implemented very strict lockdowns, so it's hard to smuggle the rhino horn in. With no buyers there's no reason to kill rhinos and dilute the underground market with it. But I could be wrong, it's just my personal idea on what's happening as someone that lives in a country with lots of rhino poaching