Very interesting - it must be due to the toughness and thickness of the leather. I found this at refinishcoatings.com:

Walrus – Leather made from the hide of walrus. Walrus hide is of such thickness that it is generally used for leather for buffing wheels. When split it is used for bag leather. It is difficult to distinguish between leather made of seal and walrus hides after tanning and splitting and the names are often used interchangeably. “Walrus Grain” is sometimes imitated on cattlehides, sheepskins and goatskins as well as on splits from hides of various animals. In such cases, the proper descriptions are “Walrus-grained Cowhide” or “Walrus Grain on Goatskin,” etc. The term “walrus leather” when used in the luggage industry is generally regarded in the trade as being genuine sealskin leather on which a simulation of walrus grain has been embossed.

Although the leather is tough it is often split into thin layers - the layer after the first has to have an artificial finish - and is then used to bind books because it is so thin, soft and pliable - it finds uses at both extremes!

Incidentally, I have been coating close-stitched cotton buffing wheels with abrasives in a similar fashion - they are very effective.

Regards,
Neil