MIMF

What is the reason many jazz guitars are using the wider 1-3/4" nut width, just wondering??

Greg, word on the street is that the wider spacing (compared to 1.680", 1-11/16") is good for fingerstyle playing. A little more room for moving around in the first position. Seems to work for me, though I have compromised and use 1.720" as a target for my guitar builds.

Also, I think some of the early archtops had the wider nut as a standard?

I'm not sure about this--there are others more expert who may perhaps weigh in on this--but I believe that 1-3/4 was a "standard" nut width, but was more recently supplanted by skinnier necks for some reason. I find anything narrower than 1-3/4 is a bit too skinny for my hands. Perhaps it's just as appropriate to ask why not 1-3/4" neck width.

Many jazz players also prefer a narrower neck. It's just personal preference for what one finds most comfortable or easier to play. One size does not fit all.

Some of the older Gibson flat tops came with 1-13/16" nuts and wider at the bridge too.

1.720 seems like a good compromise. something to ponder further.