The use of this dork dates back to the early 2000s. Early blog posts, such as those found on Jasongraphix
“The majority of the content you create should be set to allow—only private pages, such as user accounts or team pages containing personal information, should be ignored.” SpyFu · 4 years ago URL Inspection tool - Search Console Help inurl viewindexshtml
For a broader understanding of why this string works and the security implications of such "dorks," you may find these foundational research papers and tools useful: The use of this dork dates back to the early 2000s
inurl:view/index.shtml