Never said it had to be a text file. There are many binary serialization formats that could be used. But is a lot of situations the overhead you save is not worth the debugging effort of working with binary data. For something like this that is likely not going to be more then a GB or so, probably much less it really does not matter that much if you use binary or text formats. This is an export format that will likely just have one batch processing layer on. This type of thing is generally easiest for more people to work with in a plain text format. If you really need efficient querying of the data then it is trivial and quick to load it into a DB of your choice rather then being stuck with sqlite.
Never said it had to be a text file. There are many binary serialization formats that could be used. But is a lot of situations the overhead you save is not worth the debugging effort of working with binary data. For something like this that is likely not going to be more then a GB or so, probably much less it really does not matter that much if you use binary or text formats. This is an export format that will likely just have one batch processing layer on. This type of thing is generally easiest for more people to work with in a plain text format. If you really need efficient querying of the data then it is trivial and quick to load it into a DB of your choice rather then being stuck with sqlite.