I may be a bit cynical, but at least in my former field (experimental physics), the main purpose of papers seems to be to "lock in" a finished achivement. You do the actual research, pass internal reviews and peer review, and then publishing the paper is just to make it "official". Unfortunately, many papers are never expected to be read. The crucial information exists, but you usually get it from personal communication, internal wikis, or review articles. You just need the paper to copy a formula or graph, and to cite it in the end.

There are papers that are well-written and useful, but there are at least as many that are just drivel (I probably contributed to both kinds).

Unfortunately, the prevailing attitude is that outside people will not understand our stuff anyway, so we often make no effort to make papers understandable, or to publish data. (There is a lot of great outreach and science communication, but not so much for students or researchers from other fields who want to follow the technical details.)