Because...it is in an Bundle?
Users may not submit individual keys from any bundle. This includes either keys for activating the entire bundle, parts of the bundle, or individual keys for games.

Now is the time to read site rules

"Do not submit individual keys from bundles."

You may, however, make a puzzle and hide the key within it. Or simply post the key in forums for the first one to grab or whatever, as long as it's not in an official giveaway.

Aliens.

READ RULES?

Giveaways:

The submitter and winner(s) of the giveaway have seven (7) days to complete the gifting process. This includes the activation of the gift on the Steam account of the winner.

Please note you cannot gift games from your Steam library. They are permanently attached to your account and not giftable.

Do not misrepresent the title being given away.

Extraneous/special rules for giveaways require moderator approval. Public giveaways cannot have any special rules.

Please do not offer trades in the description of your giveaways.

Do not submit individual keys from bundles.

Do not submit what we consider exploited CD-keys.

Do not submit CD-keys that require VPN activation or methods to bypass regional restrictions.

Do not submit guest passes, beta keys (Dota 2 and CS:GO giftable copies whitelisted), or in-game items from games such as TF2.

Do not submit Steam or online game accounts (EVE, RIFT, etc).

Do not submit coupons or special Steam items, such as coal.

Only enter for DLC if you have the required base game.

You must redeem the game on the account you entered with, and may not trade it to others.

Abduction of giveaways...