Hi Sean,
Hope you are doing well. The binary files generated by MCUXpresso for the KW41Z (specifically, for BLE projects and examples) are always the full 510kB in size, as to overwrite the whole PROGRAM_FLASH memory region, even filling the unused space with a "0xFF" value.
This is done on purpose, so old code is not left behind in unused memory regions of the PROGRAM_FLASH.
Hope this helps.
Best Regards,
Ricardo