With the regulatory progress in the US, protocols can now look to ensure that value creation accrues to token holders. Using protocol revenue for buy-and-burn achieves this, but think that buy-and-distribute can be more tailored in providing a explicit income stream for stakers, received in a tax efficient way (increasing stSYRUP : SYRUP ratio) that encourages holding rewards (as shown by @fatmac numbers) and staking (almost ~50% of SYRUP is currently staked).
Also, in a scenario of exponential protocol revenue growth, buy-and-burn can result in a higher price per token, that can limit investor participation (and require the equivalent of a stock split, as it has been already done in the MPL to SYRUP conversion).
Looking for a potential better use of that 20%, there was some discussion in the previous proposal on whether it made sense to start a buyback program before breakeven (see here), but current outlook does look like it is around the corner.