The main reason for tougher rolls is the addition of extra flour. The dough for these buns is quite sticky, and it may be slightly hard to work with. However, if you knead the dough for long enough, it gets significantly less sticky and feels soft and elastic. Don't be tempted to add extra flour, just give the dough ha couple more minutes of kneading. Then flour the surface before rolling out to ensure they don't stick. We also highly recommend using cold stainless steel (or marble) rolling pin for rolling out stickier dough.