prevent by whom? agreeable poor economy is the main cause for PAF to get the best but it did get some best stuff from US and is under process of getting best european technologies direct indirect by Turkey. During high times PAD got F-16 deal nobody prevent us even French offered Rafale throw money get what you want from the best source like US/Euro in case of Pakistan but eventually it would be far better to slowly self develop.
You are saying why Indians are acting like scared little girls when Russia is selling Rd-93 direct to Pakistan instead through China.
We would like to prevent you from getting any tech whatsoever so as to degrade your military power and keep building our edge over you. Our relatively massive diplomatic clout in the world enables us to do.
You aren't getting more Perry's from US no more blk 52's and no Vipers/Super Cobras.
Even the US army surplus is mostly going to Jordan and you only managed a few MRAPS.
French denied avionics for jf-17 forcing you to get the chinese stuff. We paid for it in the our M2K MLU.
So good luck for indigenous development. But your foreign options in terms of quality are being choked off.
Even India is not having the best of the economic growth but international clout matters.