Sodium hydroxide (lye) generates intense heat. In a standing bath, that heat dissipates into the three inches of stagnant water above the blockage, rendering the chemical inert before it ever reaches the plug. You have effectively heated your bathwater, not cleared the pipe.
Over 90% of blockages are not "hair." They are a complex polymer of squalene (your facial oil), keratin (the hair shaft), and soap scum (the calcium salt of fatty acids). When soap meets hard water, it doesn't wash away; it turns into a waxy, adhesive putty known as calcium stearate . blocked bath
But then, the regression begins.