Yes, but DL is pumping $$$ into SEA and likely operating several less-than-profitable routes in an attempt to gain market/mindshare (for example, SEA to various cities in Alaska/Canada). Given making $$ isn't their only goal here.. why can't they lose some money on a route I would benefit from? :-P
A lot of the crazy routes out of SEA to AS and Canada have been quietly removed or scaled back to summer seasonal only. And most of those routes are sub 750 miles so even if they lost $ it wasn't big money.
Flying 1/2 full planes or for sub $200 2,300 miles to PHL is a very different story requiring a much larger aircraft.
I could see this one day when DL gets their A-220 fleet up to 90 or so