There would need to be monetary incentive for that. The only ethical way of doing so would be for all member states of the UN, or at least the richest ones, to chip into a conditional fund (the condition being no more deflorestation/reflorestation) of enough value to offset the incentives of developing the land. That's not likely to happen, so environmentalists are trying to look for other methods to do so, like carbon credit, reforesting unused lands outside the amazon, and incentivizing eco-friendly/better industries and agricultural production (biomedical research, nature tourism, more sustainable forms of farming)