Homebrewing - Beer, Mead, Wine, Cider

Fermentation is organic substrate like glucose->other things, anaerobically. You don't get alcohol without sugar being converted to ethanol. The bacteria or yeast doing so can have different byproducts depending on substrate and the fermenting organism(s). Now the more complex sugars present in a fibrous fruit like pineapple does probably result in more sugar left than usual. Additionally pineapple acidity may also reduce the direct fermentation capability. If you do as with grains where you cook and macerate it and/or increase the pH some you'd probably be able to reduce the leftover sugar sweetness more while increasing the alcohol and sour notes.