DL has had service to TXL off and on since it bought the routes from Panam (over 10 years ago). Usually one-stop via Hamburg or Copenhagen to JFK, so DL has a long history with this route and maybe some cargo connections. It was also a light pax load for DL but the cargo made it a profitable route in past years. BA used to have a German operation (Deutsche BA) which failed so OW is not too keen to go up against LH again -- and Berlin is a hotbed of LCCs but none fly trans-Atlantic yet.