Why LGPL when the original license is more permissive? (https://sourceware.org/bzip2/manual/manual.html)
The author of bzip3 probably doesnt like pushover licenses so made user rights stronger
Please stop questioning people's choice of license.
If you don't like it, you're entitled to not using it.
bzip3 is not made by the same author as bzip2, that's why there is a licence disparity.