Pretty sure it's not a "drop in the bucket" (somewhere around 20% I read?). There's also a massive opportunity cost when you consider the profit to be made from an arms race in the middle east should the US treat all countries in the region equal when it comes to arms sales. Pretty sure that would net far more for your military industrial complex than the long standing preferential Israeli treatment. It would also obviously be disastrous for Israel, so that's some serious leverage. (Note: In case you think I'm promoting this idea, I actually believe ANY arms sales to the region, Israel included, has been a horrible policy).

The US and Israel are in bed together for better or worse. It's actually really embarrassing that Israel has allowed NSO Group to operate at this level, and influential US politicians could destroy NSO Group in a heartbeat if they actually wanted to.