Muscles maintain a certain baseline level of tension by default.
When a muscle weakens, that area starts to fibrose — it hardens. That's how it secures strength. This is what a muscle knot actually is. A knotted muscle has passive tension, but it can't produce tension through movement.
So the areas that knot up actually need strengthening exercises. Massaging them loose doesn't accomplish much. They were weak to begin with, so the body needed them stiffened and fibrosed them to secure strength there.
Don't try to undo all the knots at once. The body has spent a long time securing its stability that way.