That's strange.

If you have liquid DEC on Hive Engine you should receive SPS airdrop. Here is a special notice in official paper:

Splinterlands assets (DEC, cards, packs, land claims, etc) held on external platforms including Steem Engine, Hive Engine, WAX, Tron, BSC, and Ethereum will all still be eligible to receive airdrop tokens based on the mechanism described above without having to transfer them back into the game, as will DEC tokens staked in any of the currently available liquidity pools.

However, if your DEC are locked in orders on Hive Engine you are not eligible for the airdrop rewards:

Please note that DEC or other game tokens listed for sale on external bid/ask markets (not liquidity pools) such as Steem Engine, Hive Engine, and TronTrade will not be eligible for the airdrop rewards.