Morals and virtues are sui generis (self causing) isn't that convenient?

According to pure virtue epistemology, epistemic virtues and vices are sui generis. 
 (self causing)This would appeal  be the God argument ....to ask how do you know that is a 'good; thing
the virtuous fall back on metaphysics

In this way they cannot be analyzed in terms of more fundamental epistemic or non-epistemic concepts.