While I'd love it for airdrops to target solo stakers and reward decentralization, I don't think any protocol is really incentivized to do it.  If they're using Ethereum for settlement and security, from their point of view they already paid the fair market price.

Agreed, also misses the point in that pressuring protocols to give solo stakers airdrops means solo stakers don't already have enough monetary incentives from Ethereum itself. So are ETH rewards  already too low for decentralized solo staking or are there other problems at the protocol level that need to be addressed?