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I think it's older than that, even predating SQLite. Back when Perl/CGI was all the rage it was common to store data in files. But the web was growing fast and scaling files was hard. Pushing that workload onto the heavyweight RDMBS was seen as the solution, reasonably so in some cases, but that also brought the cargo culting along with it.

When SQLite arrived it got lumped in with file storage that can't scale. Rails only perpetuated what everyone was already thinking.