Because you won’t stop stretching them. Many people who have consistent hip flexor tightness would be a lot better off if they just stopped stretching them. This often provides only a temporary relief, giving just a small window of comfort. And guess what? The more you stretch them, the shorter that window of relief becomes, until you’re at the point where you’re stretching them multiple times a day for a long duration just to feel good! That’s no way to live!
To do this stretch, sit on the floor with your legs about three or four feet apart, depending on how tall you are. Make sure your toes and knees are pointed straight up. Next, take a deep breath, and on the exhale, slowly fold your upper body forward. Rest your hands on your feet, legs, or the floor in front of you and hold this stretch for five deep breaths.