Do you think that mobility and flexibility are the same things? There is actually a big difference.
Flexibility is the ability of a muscle or MUSCLE groups to LENGTHEN PASSIVELY through a range of motion.
Mobility is an ability of a JOINT to MOVE ACTIVELY through a range of motion. It also considers how far the joint moves within the joint capsule and the motor control component within the nervous system.
Mobility is essential for flexibility. If you are trying to stretch a muscle over a joint with a mobility restriction, you will get nowhere fast. The muscle will never lengthen to its full extent as the joint won’t allow it to move far enough.
If you achieve a split only through flexibility and not mobility, the effect will only be temporary. Muscles need strength and stability to maintain this newfound range of motion.
How is your mobility doing? Is this something you focus on when exercising?