Having built something similar [1], the reason I didn't use "grep -ri license" is that I wanted to generate the list of licenses for both my project and all of its dependencies. Using grep would still require matching up each project to its own license.

Another problem is that the license file doesn't necessarily state the name of the license, which is often what you're looking for. (My package compares the text of the license to saved copies of common licenses, and picks the closest match, assuming any are a good match.)

[1] https://github.com/mwilliamson/node-license-sniffer