Because he was useless pre-Yousuf sessions. There's no point saying the sky is green and grass is blue. The numbers speak for itself - but he's worked hard on his game and the results are there to see.
As for Junaids, he also would like to promote Mohammad Nawaz as a Test #5 so perhaps you ought to be careful before declaring him a paragon of cricketing wisdom with all due respect to him.
The Mohammad Nawaz issue is slightly different, to be fair.
Ever since the Tests in England and Ireland in May 2018 it has seemed obvious that because of Pakistan’s weak batting and shallow bowling, the best Test option outside Asia is ALWAYS
7. Shadab Khan
8. Faheem Ashraf
Twice in three Tests they turned collapses into Test victories with the bat.
I do have some doubts about Faheem’s bowling, and I would be grooming Amad Butt in every national squad in every format in the hope that he can improve his batting and bowling. That extra 5K speed with the ball and 6 cm in height makes him have a much higher ceiling with the ball than Faheem has.
Mohammad Nawaz is there for a different reason for me.
I think that for the World Test Championship 2021-23-25 cycles the only viable specialist batsmen so far are:
Babar Azam
Mohammad Rizwan
Azhar and Fawad will be even older.
Saud Shakeel is unproven. Haider Ali and Abdullah Shafique are even less proven.
That means that there need to be contingency plans. And if the team is accepting of batsmen like Abid Ali and Haris Sohail who struggle to average 20 against decent opposition, you have to consider whether you stick Rizwan up as a specialist batsman so that you can accommodate Rohail Nazir at 6 and you just accept that 5, 6, 7 and 8 are all going to be all-rounders to give you batting depth to try to camouflage the lack of specialist talent.
If things don’t improve with the bat, Pakistan are going to have to seriously consider that the post-Azhar/Fawad world might look like:
1. Abdullah Shafique or Haider Ali
2. Mohammad Rizwan
3. Saud Shakeel
4. Babar Azam
5. Mohammad Nawaz
6. Rohail Nazir (wk)
7. Shadab Khan
8. Faheem Ashraf
9. Sajid Khan (Asia) / Hasan Ali (SENA)
10. Shaheen Shah Afridi
11. Naseem Shah
The batting - including Mohammad Nawaz - is terrifyingly poor.
But that’s why you pack Rohail and Shadab and Faheem as three guys who may well score as many runs from 6-7-8 as Shafique, Rizwan and Shakeel from 1-2-3.