gumbleby unless the lower deck is full then the upper deck is reserved for status passengers. Status includes PC Gold and Platinum, OWSapphire and OWEmerald. Sometimes it also includes PC Silver and full fare paying passengers. Partners etc are not allowed.

Since you say in your profile that you are 'Programs: QR burgundy' the reason that the upper deck is not available to you is that you are not qualified for those seats.
See a380-upper-deck-economy-seat-selection-pc-members or one of several other threads for more information.