Tightness is a sensation, not a diagnosis. It tells you how an area feels, not why it feels that way.
Sometimes a muscle genuinely is short. Often the sensation is coming from somewhere else entirely: restricted connective tissue that has stopped gliding, a joint being guarded, or a nervous system holding an area on standby.
This is why stretching can bring twenty minutes of relief and then hand the tightness straight back. Nothing was wrong with the stretch. It was simply answering a question the body had not asked.
When we look for what the tightness is protecting instead of trying to overpower it, the area usually has less reason to keep holding.