Because the data keeps matching their Business as Usual model. I think there's more recent research, but here's a paper from 2014, showing 40 years of reasonable fit: http://sustainable.unimelb.edu.au/sites/default/files/docs/M.... If we keep matching their model, we'll soon see dramatic population declines.
Also, the patterns revealed in their models are useful for understanding patterns in nature and human interaction with it.
Also, the patterns revealed in their models are useful for understanding patterns in nature and human interaction with it.