You are right that targeting swap volume also inherently targets fees. But, Uniswap’s fee-generation on Base is significantly higher than the one on Arbitrum despite trading volumes being lower.
In May, trading volumes on Arbitrum and Base were $11.59B and $5.24B respectively. Despite Arbitrum’s volumes being more than double, Base generated $9.37M in fees while Arbitrum only generated $7.49M.
It would be interesting to understand if incentives can play a role in improving Arbitrum’s performance. However, that might be out of scope here.