To load again so what is shown matches what is. Reloading discards the current state to get a true one.
Re- (Latin, again) attached to load, from Old English lad (a way, a course, a carrying), related to lead (to guide); to reload is to carry the same load again from the start rather than trust what was already carried.
To load again so what is shown matches what is. The root's carrying is discarded and repeated on purpose, trading whatever accumulated for a true reading taken fresh.