Why not? Just roll your own write-ahead log when you are writing to CSVs! That's all the SQLite code is doing.
SQLite does not selectively lock portions of the file for writes. It locks the entire file using the Operating System's own file handling services.
SQLite is a file format. CSVs, XML and JSON are also huge in the dB marketplace. That doesn't make them RDBMSs.
A collection of CSVs can be used as a database.
And I'd say that not only is sqlite in the db marketplace (albeit for a specific subset of database application types) it's one of the largest players.