I mean you can pay nodes for forwarding your onion messages if you want 🤷‍♂️. The whole point of onion messages is that they don’t cost a node ~anything to handle so there’s no reason why a node should want to charge for it. Also, with BOLT12, nodes will eventually prefer to route HTLCs through nodes that forwarded onion messages for the same payment, so you do get some non-zero expected value.