Why should one look at Sanskrit philosophical texts through a philosophical approach? Are not specialists of Sanskrit language enough? Why should one bother understanding the philosophical implications of the text?
A first answer is that these texts have been written for philosophers, and hence deserve a philosophical audience. Furthermore, a philosophical approach makes it often possible to uncover aspects of a text a non-philosopher would not have thought of.
In the case of Jayanta's Sarvāgamaprāmāṇya, this approach made it possible to consider more closely some of the elements of the text, such as the interpretation of the mahājanaparigraha. This oscillates between a quantitative agreement and the qualitative component of this agreement, which must be free of inner disagreements and involve the best part of the society. Furthermore, why did Jayanta feel the need to mention the absence of fear towards a certain religious text among the criteria for accepting a religious belief? A philosophical approach made it possible to distinguish, within Jayanta's texts, between theoretical and social worries and, consequently, between the social aspect of fear and its theoretical background, i.e., the role of emotions within epistemology. The latter aspect had been neglected in the past analyses of the Sarvāgamaprāmāṇya, and could be noticed thanks to a properly philosophical approach.
On Jayanta in general, see this post. On social and theoretical issues within the Nyāyamañjarī, see this post. On the consensus gentium in the Nyāyamañjarī, see this post. On emotions within epistemology, see this post.