Because Edinburgh is well/over served transatlantic, as is Glasgow, so it makes sense the low number of flights from Glasgow and none from Edinburgh. If people want to go to New York they'll go United, or Delta or American... Or Norwegian... Even without NAX, It's pretty much a saturated market, but why should that stop EDI throwing airlines and seats at their routes?
For Jet2 though, it strikes me that it probably wouldn't be worth it the way they operate it, with the long EWR layover etc.