possibilities:

1.) the sage is insane
2.) the sage was cold
3.) the sage read s/he should do this
4.) there are no books; this is why they are named books
5.) words by their nature are limiting
6.) to build a bigger head over his head
7.) empty
8.) the sage didn’t really burn his books
9.) the books had expired
10.) the sage was a liar who never had books
11.) reads majicks in the aether instead