Answer:
I think a unicorn would lose its horn due to poachers and hunters. Poachers often cut off rhinos horns. These are usually used as a status symbol or in certain types of medicines. I presume it would be the same with a unicorn, especially because it is a mythical being. Its horn would be taken for a status symbol. Because it usually has magical properties, it could also be used for medicines.
Hope this helps <3
