Rangers are often from the same village as the poachers. Sometimes the same family. Rangers often know who the poachers are, (we're generally talking bush-meat type poaching now), so will only shoot them if they absolutely have no choice.
Please stop falsely conflating meat poachers with rhino horn poachers. Poaching for the pot makes up a very small proportion of
rhino poaching; less than 3%. No-one here is talking about bush meat poachers except you. The poachers killed by those lions were
rhino horn poachers, and that is the only thing we should be talking about here. These three cut their way into a fenced off wildlife reserve to kill rhinos for their horn. Nothing else.
Rhino horn poachers are almost never spear-carrying local villagers living in grass huts trying to scratch out a living to feed their families. They are professional poachers employed almost exclusively by organized crime syndicates. They are extremely well paid and very well equipped with military type materiel. They have been seen carrying and using assault rifles such as the AK47, sometimes fitted with under-barrel grenade launchers such as the GP-25, or GP34. They have also been seen carrying RG-6's, Russian made 40 mm semi-automatic, six-shot revolver-type grenade launchers, as well as night vision goggles and helicopters. They come in from cities such as Polokwane (Pietersburg) and Mbombela (Nelspruit) and even from the larger cities of Johannesburg and Pretoria, as well as coming in across the border from Mozambique and Botswana.
Rangers are often poachers themselves. Blue Lagoon National Park, Zambia, was just about poached out by the rangers stationed there 10 years ago.
Again, NOT rhino horn poachers, and this certainly has not been not the case for at least 20 years.
Poaching rhino for the pot, while illegal, is sustainable. Poaching for horn at its current rates is not. The population of Black rhino has dropped 97.6% since 1960, the vast majority of this has been in the last 15 years
THIS is how serous the problem has gotten.
As you can see, the rangers have ben slowly getting on top of the situation, but they will have to be quicker if this endangered species is not to disappear with a human lifetime.