The C in DMCA stand for Copyright. All (I think?) software licenses are underpinned and made legally enforceable by copyrights. EULAs are underpinned by licenses which are founded on copyright. Patents are the only one of those protections that are not based on copyright, and there are lots of very good arguments against at least most software patents (all software patents of the form "Do {well known and obvious thing} with a computer" should, in my opinion, be immediately revoked and potentially have every company who's enforced payments from such patents investigated for fraud).

You may recall that the DMCA was originally written to protect music and movies. It does in fact apply to creative works. If you have ever purchased an MP3, eBook, or streaming movie, you will also be aware that you purchased a license to the underlying IP. This is also true of physical media, but the license agreement you have to accept when obtaining a digital work makes this explicit.

I agree that you can't patent a book, but I would point out that you can patent an idea, which may only appear in a book or journal article.