I do not know the full circumstances of the demise of OnRisk but I always assumed that the sad death of the company founder must have played a part. I would also contend that AIG, who underwrite the Visicover policies, are a very different beast from the underwriters behind OnRisk, one of whom I believe was based in Northern Cyprus.
The big difference is that the pricing differential on the Visicover model comes from the fact that it is an entirely online service. This provides a radically different cost model from traditional aircraft insurance provision, and it is this which mainly funds competitiveness, not simply rate cutting. Thus the underwriting performance of the book is less at risk.