Aquarius is designed to supercharge trading on Stellar, bring more liquidity and give control over how it is distributed across various market pairs. It adds incentives for SDEX traders ("market maker rewards") and rewards for AMM liquidity providers.
What is the biggest group aligned with the Aquarius mission of bringing more liquidity to the Stellar network? The answer is simple — the holders of the native currency of the network, Stellar Lumens.
Therefore Aquarius is airdropping 15B (15% of the AQUA supply) to XLM holders.