They explain the distribution here:
https://shapeshift.com/shapeshift-decentralize-airdrop. In short, most of the airdrop is for their platform users (which is not surprising), while the rest are for others who use ETH defi ecosystem such as Uniswap, Sushi, etc.
I think the fact that they decided to be a decentralized project is one of the proofs that suggests they're not running that well. So this switch might be the best thing for them. Whether they can compete or not, will be decided by the market. Even if they fail, I don't think the impact would be that huge. If anything, the team should be the one to think about this.
I've never used Shapeshift in my life, but my ETH address was still eligible for the airdrop. It's probably because of my participation in Uniswap since the beginning of the year. The fact that Shapeshift went from being a centralized exchange to a decentralized one tell us that it wasn't that much of a success as one would thought it would be. I wonder how the Shapeshift team will be able to make money by decentralizing everything? The move could be related to regulatory pressure from mainstream governments. By becoming decentralized, Shapeshift would become "immune" from government regulations. At least, that's the way I see it. But I could be wrong.
Now it's a matter of time before Shapeshift competes directly with already-established platforms like Uniswap and PancakeSwap. The team needs to give their all in order to make the project a success. Otherwise, it'll go down the drain as its competitors gain traction in the mainstream world. Uniswap is the biggest decentralized exchange in the world right now, so I doubt Shapeshift will be able to challenge it in the future. I wouldn't worry about this since the more decentralized exchanges there are, the more crypto/Blockchain tech will be able accessible to everyone. Just my thoughts