I check with google flight and Delta on a daily basis.
Flights mentioned above are for a basic ticket with no checked luggage and no seat selection.
In addition they have one connecting flight.
Also some of the airlines offering lower prices tend to have super long connecting times or terrible departure/arrival times.
The last two years I flew with Delta non-stop and realized how much more convenient and stress free it was than having to fly to one location, get off a plane, wait maybe several hours, get on board another plane, take off and land again. What is already a long day/flight becomes even more so when you have a connecting flight to deal with.
I am willing to pay more for a non-stop but not hundreds of dollars/euros more.
I check daily and will wait and hope prices come down to something I feel I can manage.
It is still 8-9 months before I usually leave for Greece.