DL usually only does a mid-flight "snack" if flight is usually 12+ hours.

SEA-ICN is just under this. DTW/MSP/ATL-ICN all get (or should) the mid flight snack. Usually something like a cold meat tray or slice of pizza, noodle dish, etc...

GUM is part of US. DL can sell a ticket ICN-GUM. Booking separate tickets when flying US-GUM can be tricky. If OP had booked KE metal SEA-ICN (even Via DL) they would've needed to wait at least 24 hours in ICN before KE could legally fly him on KE ICN-GUM. (Even on separate tickets it is illegal, and KE has systems in place to detect this) Otherwise they violate cabotage laws.