I’m not sure it’s that simple, though. There’s an inelastic demand for some of these things. For example, no matter how many other opportunities you provide lion and elephant poachers in Kenya, for every poacher you take away that will drive up the cost of a pelt or tusk, making it more lucrative once more.
It helps to think of poaching vs preservation not as actions of individuals, but of communities.
In Africa, for example, tourism has become a major economic force in many rural areas, with rare animals being central to the attraction. Since those communities are as tight-knit as they are in small villages anywhere, they have both the incentives and the means to stop individuals from undermining the local economy.
It would certainly go a long way to help, though.