Tanning a sheepskin with marine oils to produce a chamois is essential to the process of preserving the leather and converting it to the soft absorbent material a chamois cloth is prized for. The marine oil reacts with the protein structure of the skin in a manner that reforms the protein chain from a linear, flat, tight fiber structure to a multi-dimensional protein fiber that is open, and spongy. And it is that multidimensional protein fiber, or spongy material that makes the cloth hydrophilic or water absorbent. No other tanning agent has that ability, only marine or fish oils.
All other tanning agents react with the skin to produce a leather that is water repellent rather than absorbent. And these are used to create other types of leather products, more appropriate to their use. After all, no one would want a leather jacket, bag, wallet, or pair of shoes that absorbed water.