that's not what the name implies. Gross simply means large or super, as in Super-Market or in Bulk-Sale. Originally it has also meant rough. In English it still does, but formerly in a sense of coarse, and I guess in this case especially rigid.

> ... Its meaning forked in English. Via the notion of "coarse in texture or quality" came the senses "not sensitive, dull stupid" (1520s), "vulgar, coarse in a moral sense" (1530s). Via notion of "general, not in detail" came the sense "entire, total, whole, without deductions" (early 15c.), as in gross national product (1947)

https://www.etymonline.com/word/gross

Okay, not quite rigid, but not either dull, stupid. It's actually difficult to believe the outline, while the beginning is uncertain.

A gross may also have meant a dozen, and Groszen was a coin, maybe a dime a dozen. So, what are these twelve products that estimated national domestic production there and then, metal, salt, textiles, big macs?