If you aren’t cognitively aware of what you are trying to accomplish (education) and you cannot self-correct through proprioceptive awareness, then you cannot achieve the proper postural alignment necessary for good mobility. Many “stretching” routines fail to accomplish anything because the foundation awareness and alignment are missing.
Most people are not adequately educated regarding the development of functional mobility. Online and written instructions on “stretching” do not teach and train anyone how to perceive what their body is doing; nor do they usually explain why a particular position is being used. This typically requires some hands-on instruction, something most physical therapists do not have time to do and something most personal trainers/strength coaches don’t know how to do. These positions need to be practiced and occasionally tweaked with manual cues and feedback.
Last, but not least, mobility is best gained by using gravity-based postures that mimic functional movements and/or address negative postures/mobility deficits. For the lower extremities, this means keeping the feet on the ground, keeping the torso upright and monitoring the pelvis/lumbar spine at all times.