The first reason is that it’s 150+ pages long, and for documents of that length, in Anno Domini 2004 paper is a superior delivery technology. I’m sure that’ll change, likely in my lifetime; whereupon our much-loved book collection will start to become increasingly like my much-loved vinyl-LP collection, in a bunch of interesting ways.
The other two reasons are quotes that I stumbled across in scanning the first few screens-full of his introductory chapter. Reproduced without comment:
And it is a mistake to think that a mathematical idea can survive merely because it is useful, because it has practical applications. On the contrary, what is useful varies as a function of time, while “a thing of beauty is a joy forever” (Keats).
Well, the computer changes epistemology, it changes the meaning of “to understand.” To me, you understand something only if you can program it. (You, not someone else!) Otherwise you don't really understand it, you only think you understand it.
(Mind you, that second quote also highlights Prof. Chaitin’s love of exclamation marks, which infest his text like ants in a picnic basket. There are worse things!)