First of all, keep in mind I hold ROOK and would benefit from LM, so I am biased.
The first thing I'd like to point out is that the proposal to add LM to the ROOK pool should not be bunched together with the proposal for bBADGER and bDIGG. ROOK is the governance token for KeeperDAO and has respectable daily volume:
Now on the other hand, bBADGER and bDIGG are not the base BadgerDAO tokens, instead they're the tokens you get back from staking them on their platform. These aren't tokens you can find on CoinGecko, for instance, as no one really trades these. So the case they are making is that by providing liquidity, people *could* start trading them. It's a big if, and they do not actually need LM to prove this theoretical volume exists. From my point of view, they should get together and fill those pools to the brim and prove there's an actual market for it. Only then would it make sense to incentivize them to keep it there and add more through LM.
When it comes to ROOK, a decent amount of the daily volume is already being routed through Bancor (currently over $800k), but most of that comes from large orders through aggregators like 1inch where only part of the order is sent to Bancor, because Uniswap is still the most liquid pool ($13.8M vs $13.1M on Bancor). The argument for adding LM to ROOK is that it would undoubtedly flip Uniswap and a lot more volume should start getting routed through Bancor because Uniswap providers would move over and slippage on there starts becoming an issue.
Whether this flipping of liquidity is worth it, I don't know, but it's quite a different story from the bBADGER/bDIGG LM proposal that to me is a clear case of greedy people just wanting to double-dip rewards: the ones from the BadgerDAO platform and the ones from Bancor.