Pakistan is a poor country, it has widespread poverty and can’t fund decent health & drinking water for most of its population. It’s military would lose a war with India, even if it used the A-bombs it has.
Buying more submarines is useless vanity and Red China is no real friend to Pakistan, China just wants to scare India a bit. Taking on debt for water toys is a dumb move for Pakistan.
Pakistan wouldn’t be existing today if it wasn’t for Chinese political, economic and military aid.
The 1st submarine kill after the 2nd World War was by a Pakistani sub, so their subs aren’t exactly going to be useless.
Pakistan isn’t sane.