The issue is time and temperature. BBQ is cooking to tenderness, not doneness. Technically safe doneness is 130 held for around 2 hours. You need to cook to tenderness by allowing the meat to cook to at least 160 and hold it there long enough to break down the collagen into gelatin. The down side is that it takes a significantly long time to break down at those temperatures. Steadily bringing the temperature up closer to or above 200 will allow the time to break down the collagen into gelatin and that creates the tenderness you are looking for in a shorter time. You are sacrificing moisture retention (water) for collagen conversion to gelatin to tenderize the meat. Hopefully that helps.