because Pakistan is not arming enemies of Israel, and enemy's friend is also enemy. Israel is not just usual military equipment seller like others, it sends its professionals to provide support during hostilities with Pakistan, also training in IOK which other countries don't do.
This big crap will only be credible when Israel will not receive any support from its western allies in conflicts.
Do remember Israel have not scored any kill against Pakistani pilots in even or uneven fight till now, while Pakistani pilots have killed many Israeli jets during arab war.