I happened to wonder about same - though with syslinux instead of extlinux - lately, but a look at included 'news' would explain:
* core: Split non-core functionality into ldlinux.c32, which
is an ELF module loaded by the core that contains everything
the core doesn't require to boot the system, e.g. config
parser, command-line interface, etc.
Also, I think the resulting size of the 2 commands you posted could not directly compared, as only in one of them you used the "-s" option.