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the acids in the pineapple apply to square cube law; alongside that, the steak is grainy & filled with voids, so it soaks up the juice to an extent
you can also do this technique with blueberries too; vinegar also works, but obviously imparts a vinegary taste 
perhaps you could try using one of those pokey tenderizers, poke a bunch of holes in it, and leave it for a shorter amount of time? 
experimenting with different acids & fruit could be quite interesting too