The main 2 reasons are :
1)Degradation Problem
The most significant loss of vegetation has been in the over 470 million hectares of rural managed land that has been farmed at various intensities, with around half of this being variably degraded.Land health is at further risk from changing land use, changed water and fire regimes and overgrazing. So this is considered as a serious problem.
2)Climate Change
Climate change is providing new challenges to wildlife exacerbated by reckless development and past abuses. Hundreds of thousands of miles of roads fragment habitat and irresponsible actors threaten wildlife by poaching, overharvest of fish and wildlife, using All Terrain Vehicles on sensitive landscapes, and introducing invasive species.
Apart from this, Public agencies charged with managing wildlife for all citizens are struggling to carry out their conservation mission due to dwindling budgets and political meddling.