Why don't animal rights activists start farms to help raise the endangered animals they want to protect?

Farming is the best way to protect a species, Animals who are being farmed normally provide an economic value to those who farm them. WE grow chicken because we want their meat, eggs, and feather, We farm cows, sheep and goats because we want their meat, skins, fur, and milk. Not only do farms protect the animals being farmed but the sick, deformed or those with bad genetic makeup are culled which means that the species becomes stronger genetically. Say I want to sell ivory. I could go out and hunt the elephant or look for the dead ones or I could start an elephant farm where I can raise huge herds, cull the ones that genetically mutated, become ill, or injured and within 60 years I would have a steady supply of ivory without endangering them. Not only would I have plenty of ivory but I can make money by offering elephant rides. This would result in elephants not being endangered and having the top genetics. This could be done with Rhinos This would reduce the incentive for poaching as a steady supply of Ivory would mean the market price for ivory would be more stable . If this was done with all animals we would no longer have endangered animals. This could also be done with plants, The best way to save endangered animals and plants is to farm them.