"Failure" in terms of producing any empirical support, that is, while its proponents have been predicting confirmation any time now for literally decades. See the example links I provided on this. It has now largely retreated these claims into an inscrutable and non-falsifiable "landscape" of possible theories, such that the question of whether it any longer qualifies as a scientific (rather than mathematical) endeavour has become legitimate to ask.

The residual feeling that academic recruitment and budgets have been dominated by what essentially turned out to be physics vaporware is a large part of the perceived crisis that Caroll doesn't appear to want to fully acknowledge.