1. get an empty Eternia box
2. fill it with other parts, pack it sufficiently to be full but not overstuffed (of you've seen an Eternia get opened, you know all the parts are Tetris-ed in there very specifically and there is little-to-no wiggle room)
3. seal it with the kind of tape that is just the right amount of yellow and dried up in places, yet totally sealed and lined up correctly just as it is in pics of sealed Eternias (Eternia boxes are primarily taped, not glued)
Not to mention the profit margin in that sort of 'forgery' would be pretty sad once you account for how much time and effort went into it.
It seems disingenuous to mock other people's sealed box preference for a whole paragraph and then try to pass it off with "thats just me. to each his own". If you think other people are making a mistake in their collection, that's fine, but it does no good to bash other people's preferences here on our public, shared forum.
Your pair of loose Eternias sounds awesome, glad you have an Eternia in the way you prefer.