This logic is flawed. X is not in Y, so we shouldn’t add it, because currently in Y no one is using neither X nor some crippled parody of it.

It helps because apps are often used to view or edit files. By “files” I mean things like word doc files, photoshop files, Apple Keynote files. Many people like working with files and saving them locally, rather than on a server. With SQLite running in the browser, a file that is an SQLite database can be very easily read into memory, worked with, then saved back to disk. The page I linked explains this in detail. There are some examples of companies taking this approach at https://www.sqlite.org/appfileformat.html. Hope this extra detail is helpful.

Edit: Additionally, I encourage you to experiment with this. If you haven’t already, you may be surprised at how efficient/compact SQLite files are. They’re significantly more compact that JSON or XML documents and can include binary files like images. It’s much simpler to use SQLite as a file format than to create a custom binary file format.