What am I doing wrong?

I smoked a brisket yesterday at ~250 for 10.5 hours. It was unwrapped for about 6 hours and then I wrapped it for the finish. When I took it off and went to cut it, the layer of fat was almost fully intact and not melted like I would have expected it to be. This same exact thing happened to me with pulled pork last time I smoked it. The meat had great flavor and was fully cooked, just not near as tender as I would have thought/liked.

Am I doing something wrong? Is there something wrong with my smoker? This has never been an issue until the last two smokes.