It started off as an experiment almost 10 years ago[1], to see if it was possible -- and it turned out it was. AFAIK rqlite was the first time SQLite was combined with Raft, though many similar systems followed, created by other developers e.g. dqlite.
Over time rqlite has became a much more substantial database than it originally was, with a focus on ease-of-deployment and ease-of-operation. I have written a fair amount about how the design and implementation has evolved over the years[2], which may be of interest.
[1] https://www.philipotoole.com/replicating-sqlite-using-raft-c...