Data Used by the App

I have releatively recently (within the last few months) downloaded Chess.com's app, and have been fairly pleased with it.  That being said, I am puzzled by the excessive (it seems to me) data it uses.  I do not play "live", and make about 1-3 moves a day, which usually takes somewhere in the order of megabytes.  This isn't really a problem for me, I am simply curious: why does it take so much memory?

Every chess game starts in a default position, and every move can be transmitted in (less than) two bytes.  Following this, when I check on a game and make a move, it should take less than a kilabyte (even for ridiculously long games).  Even for ease-of-programming, let us say that the app also sends the position explicitly (and that the previous moves also need to be sent).  Then we just add a cost of about 512 bytes.  Even passing about 600 bytes every move though, a 60 move game should still only take about half a megabyte.

And this is about as inefficient as it seems reasonable to get.  I don't develop apps, but it seems entirely reasonable that a 60 move game could be coded so as to require less than a quarter of a kilabyte (the app can just store the previous position, requiring only 2 bytes per move).

So my question is this: what is using this extra data?  Are the images for the pieces passed every time I look at a position?  If so, can these not be stored in the app itself?

Thanks.

This has been reported to the developers to check out, thank you!

Thank you :)

I should clarify an ambiguity: it is not taking megabytes per move, but per game.