A lot of folks actually don't like those big margins, feel they waste space that could be more profitably used to display text and the like.
The other usual complaint is font size, which is another preference thing. The most telling comment on the formatting is mainly that there's not really anything much
done with the formatting: the books are largely as you can download them
for free from Manybooks.net, and that being the case, many folks feel it's a bit disingenuous to charge for them.