Simple as that, despite lichen being a veggie, you can't feed it to a beefalo, a pig, or any other mob. The prompt doesn't show up.
Pigs will still eat it off the ground though:
This is due to cut lichen lacking the "tradable" component.
1. c_give("cutlichen") c_spawn("beefalo")
2. Try to feed the beefalo the lichen
3. Notice the prompt doesn't show up