We started throwing a ball for Willow out on walks as you see other dogs doing all the time. At first she was really good and even dropped the ball at our feet when she wanted to us to throw it. After a while she realised she was being put back on the lead now she runs out reach when she has a ball. She has really good recall and doesn't stray too far when off the lead. I only give her the ball if she is on the lead throwing it so she can catch it even then she is reluctant to drop it or give it back and treats don't work as the ball is higher value.
It's a common problem, but one that there are training solutions for! You can find a guide to dogs that don't bring the ball back here. There is information on the clicker trained retrieve here. Hope it helps
If Willow would drop the ball for a treat this would work so I will take 2 balls and only throw one when I have the other. The issue is she sees the fun ending when the lead goes on so refuses to come to me when the ball is in her mouth.