IIRC from a while ago on here, DL.com wasn't offering award options with more than one connection to get to SYD from the U.S., so you had to be at an airport with a nonstop to LAX or you had to book the award out of an airport with a nonstop to LAX and position there. You could be running into this issue (annoyingly) since no D.C. area airports have nonstop to LAX.