Because it's not important. What is more important is that the First Science Sequence was finished. In a detailed report, you may find that the battery didn't last as much as they thought it did (perhaps because of the double landings Philae had to make, etc.), but a public-facing article is not the place for it.

Also, there are probably N things that didn't happen as they thought it did. It is better to mention the K important things (K << N), than the N unimportant things that they got wrong.

If Philae, for example, didn't land on the comet at all, then they would have announced something like this: "Philae took a drive-by of the comet 67 p, and has done in-air experiments that would be valuable for us".