Hi all - infrequent Delta flyer here so apologies if this is a basic question...

Am flying in a couple of weeks JFK-MEX. Seat map shows 9 open first class seats and indeed Delta app shows 9 first class seats remaining in the 'Upgrade & Standby' section. However looking at expert flyer, the flight shows J2 and indeed if I search for 3 seats, this flight shows as unavailable in first class on Delta.com.

Anyone know why Delta would hold back so many seats from sale? Flight is in 2 weeks so not COVID seat-block. I am of course hoping the reason is an anticipated equipment switch to the 757 with lie flat seats (although even then, they are holding back from sale more seats than necessary).

Anyone have an explanation? Flight is DL603 on 5/14.

Thanks