Why the BIG Price Difference? Seaview

I was looking at November 2018 cruises and came up to what looks like a good deal to me, but might be missing something.

For November, all 7 night cruises on Seaview start at $708 pp,

but there is one sailing that is 6 nights that starts at $379 (with 5%), it has since sold out...but OV and Balcony are still available for around $1K for 2 people.

Yes, it's one less night, but the price is amazing...unless I am missing something?

Wanted to add they had a YC suite for only 1200 pp, but it has since sold out...I guess people are noticing this deal and booking...which leads me to book before these prices are gone...in 2 days, insides and YC have been sold.

yes the pricing is odd ive just booked from the UK for the 6 night cruise from Naples and yes its almost half the cost of the 7 night cruise !!!!!!!!!!!!!! great price for a balcony