Doesn't surprise me, I was reminded of the Drizzt cameo in Baldur's Gate, where he kills dozens of gnolls, when I saw the movie. You could replace Xenk with Drizzt without affecting the story at all.
But it was the right decision, Drizzt is decidedly unfunny, has no name recognition outside hardcore D&D fandom, and inside the fandom is hated by as many people as he is loved.
Drizzt would not have been as good a fit to the tone of the movie, certainly. While they could've done the same schtick with Drizzt as Xenk, playing him completely straight as an overly angsty, edgy, and broody character, I think it wouldn't have had the same comedic weight. And could've potentially backfired by feeling more like they were making fun of him.