It was used for small things like ... well, garters obviously, and I think I have seen caps and a muffler in pure garter stich, probably because it is warmer. It was also used for decoration, see for example the Gunnister man's gloves.

I would do the hat in garter stich anyway. Fashion was rather wild back then and we have only few real finds from that period and most of them are from only a very small stratum of society. If it looks good, then I'm sure somebody might have done the pattern in garter stitch as well.

Only I have a sneaking suspicion that it might have been considered lower class knitting, not done by a professional knitter.