Because I want to. Because I am now old enough to meet some of the characters (Pierre) with less sympathy than when I was a student.
The translation I am using is Project Gutenberg EBook #2600 (posting date January 10, 2009). The text version says the translators are Louise and Aylmer Maude. So far it seems much easier to read than the Rosemary Edmonds translation in the Penguin Classics version I first used in college in the Great Books program back in the 1970s. The Maude translation for the Kindle has some of the trickier French phrases asterisked and translated in a slightly different font at the end of the current paragraph, rather than having to click a footnote. The Maudes' English seems more free of affectations of haute couture than Edmonds'.
I love my Kindle. Kindle Keyboard 3G. I can embiggenate the text. The effect is much easier for my eyes to focus on. Plus the Kindle text is black on white, not grey on beige (in 6-point Badly Kerned Olde Booksquiggle).
At well over half a million words, War and Peace is a big book. But the title (and the content?) must be more intimidating than the size. It's shorter than Atlas Shrugged, and there are plenty of people who are happy to buttonhole you and tell you all about Atlas Shrugged.
Anyway, I'm having fun with it.