The full form of FITS is Flexible Image Transport System.
Which is much more flexible and come with lots of convenient and fast api.
Better than the self-defined file format, tsv file.
The most of all, astronomical software usually deal with fits file.
In the future, maybe tat python need to adjust its system to fit another system, it would be easier.

spec

1. file format is fits.
2. datatype is table, defined by astropy.table