Delta would use old aircraft on this route
Delta uses old aircraft on most of their routes. That's been their MO for a while. Delta was the launch customer for the DC-9 in 1965 and retired the type in 2014. COVID accelerated the retirement of the derivatives (MD-80/90), but they're still flying the 717 (a.k.a. MD-95).The last time I flew SFO-JFK I was on a Delta 767-400 and yeah Delta hasn't updated the interiors on those. Compared to other airlines that typically run a premium (single aisle) product on that route the extra aisle and the 2-3-2 seating are pretty competitive unless you're jonesing for crappy seat back entertainment.