Delta lost pretty much all of it's US-India presence the first time it dropped JFK-BOM. By the time it later inherited AMS-BOM from NW, this was no longer a preferred way for Americans to get to India/Indians to get to America as by then the ME3 had largely taken over the market, and the preference became transits in the UAE/Qatar as opposed to Europe.

Had DL stuck with JFK-BOM the first time around rather than trying to move it to ATL, my guess is that it would have continued, at least until this year.