Multiple reasons :
1) Not applying enough intensity ( just like in the gym,when a
weight is too light,you can feel it ,you're like " i need something heavier,this isn't going to make my bicep grow ) .Same thing in PE.When you stretch,make sure you " feel " the stretch,make sure it's intense enough .As time will pass,your dick will get used to the curent intensity,and you will need a even higher intensity to gain from that point.
2)You are not keeping your dick expanded/elongated after a workout.For exemple,when you stretch,you stretch your whole penis,cells,tissue,etc,making them longer,but when you stop PE-ing ( when you stop stretching,wearing an [words=https://shop.mattersofsize.com/products/sizegenetics-penis-extender]extender[/words],whatever ) this tissue will want to go back to its original form,so you have to force this tissue to stay in that elongated state even after you're done with your routine.This is why we use
cock rings to heal after girth work,and an [words=http://www.
phallosan.com/shop/catalog/default.php?z=eNortjIxtVKyL0pNszWxMFcrSSxKTy2JL0hMT7U1UisoykyxtbBQSy4tLsnPjS8uKcrMS7dVsgZcMMpbEbo%2C]ADS[/words] ( or an [words=https://shop.mattersofsize.com/products/sizegenetics-penis-extender]extender[/words] at light tension ) to heal after length work.Read the [words=http://www.mattersofsize.com/forum/showthread.php?64036-My-Best-Work-Ever-Penis-Enlargement-will-Be-Changed-Forever-gt-gt-Gain%20inches%20with%20SRT-Theory-and-Routine]
SRT[/words] to understand this better.
3)Stretching and jelqing are pretty much basic PE.I'm not saying you can't gain from this,i'm doing PE for years and still have jelqing and stretching in my routine,but if you want to gain fast,you have to buy some devices,or to switch to more advanced exercises.
4) Diet,sleep,stress,etc : If you want your dick to grow,you need to take care of your whole body.If your body is fucked up,this might slow gains.
5) You are a slow gainer : I didn't really belived in this slow gainer thing,until i realised how hard is for me to gain length..girth,i gain it VERY easily,length,not that much.I have to use intense length routines to gain length.So you might be a slow gainer,you just have to be patient and the results will come,a bit hard,but they will come.