If you opened this post, chances are the muscles on the front of your legs are having separation anxiety. They will never let go and tend to get even angrier after a long day of walking/sitting/standing.
So why are your quads always tight? The easier answer is that we place the weight in our toes versus our heels which keeps these guys engaged regardless of whether we sit, stand or even walk forward. The brain is a creature of habit so the more we maintain this repetitive posture, the more it knows to turn these muscles on.
So it is a bit misleading to say that stretching the quads will actually teach them to let go. A better thought process is that building time in postures that give us different inputs to the brain will do the same.
That leads me to two of my favorite drills to do just that: wedged standing and quad sit. These two things have helped me to turn off my own quads for years by simply building time in these positions throughout the day.
PS: Quad sit hurts like hell in the beginning, so you can use a pillow or yoga block behind the heels and build to a deeper depth as things become easier. Perform the first exercise in the article and sit in it rather than moving.
I hope you enjoy and let me know if you have any questions!