Apologies, yes LAX is not a DL hub, it is a focus city. Nevertheless, I meant that they probably ha

There is an everyday 777-200LR flight, Delta 16 usually, that flies from LAX-ATL. This is after it s come over the pacific from SYD. It makes sense for them to put passengers on the flight, more revenue. Also, LF numbers are pretty high, 777-200LR leaving on 12/13 is ~98% booked. It s probably all of these factors, the 777 is a very capable aircraft and Delta exemplifies that.
While the gate argument is possible, if Delta sees the need to drop a 777 on an ATL-LAX segment because bookings are strong and additional revenue could be realized and an aircraft is available, then I m fairly confident that they would do it. A 777 on a route like that could very well mean an increase in demand.
A 767-332 can be filled at 90% load factor on most ATL-LAX flights. Putting a 777-200 is not because their is demand, but rather a way that DL can increase fleet utilisation. It makes no sense to put a 777-232ER on LAX-ATL, but it makes less sense to have one sitting at ATL wasting gate or ramp space. Wasting gate space means that s one less flight that could have brought in paying passengers.
Apologies, yes LAX is not a DL hub, it is a focus city. Nevertheless, I meant that they probably have quite a bit of feed on the route and that may be part of the reason they put a 777-200 on the route, or of course it may be just because the A/c is needed in ATL.