The flip side to this is that Al Qaeda had a clearly stated goal which was centered on targeting the US. It would be like me donating money to the PIRA and hoping they don't attack British targets...or not caring...
Well, clearly not everyone in Saudi Arabia was on board with the Saudi-US relationship, least of all Osama bin Laden. Saudi Arabia (and other Gulf monarchies) for that matter) at every level from the royal and religious elite down to ordinary pious Saudis had showered Osama and his Afghan Arabs with donations and other support for his anti-Soviet jihad. Not that he was a particularly important actor in Afghanistan, but it was enough that a young man from an incredibly wealthy and prominent Saudi family gave up a comfortable life in the Kingdom to go help his Muslim brethren in Afghanistan.
Osama bin Laden was a rock star as far as Saudi Arabia was concerned in the 1980s. After such a massive, decade-long investment not just in bin Laden's efforts but the broader anti-Soviet jihad in Afghanistan (with the Saudis funneling money, with the help of Pakistani intelligence as well as more directly, to the most hardline of the
mujaheddin), it seems unlikely that the conservative and risk-averse House of Saud would have done a
complete about-face (covertly, not overtly). Epecially once bin Laden and some of his battled-hardened Saudi volunteers returned to the Kingdom after the Soviets were driven out and King Fahd made the incredibly controversial decision to station American troops in Saudi Arabia ("we don't need the help of the American infidels to defend the Kingdom from Saddam!", bin Laden vented to Saudi officials, to no avail).
By the mid-1990s, when bin Laden really started to escalate his newer anti-American (and anti-Saudi royal family) jihad, the House of Saud was too fractured and internally divided to fully control the Islamist dissidents (many of whom, again, had previously enjoyed massive support - people like Osama bin Laden). King Fahd was paralyzed from a massive stroke in late 1995, jealously guarded by his wives and sons, while Crown Prince Abdullah struggled to crack down on corruption and make headway with other cautious reforms and the King's full brothers, in charge of the Interior Ministry (Nayef), the Defense Ministry (Sultan), and Riyadh Province and the Royal Court (Salman, who is now King of course) were opposing Abdullah at every step of the way.
The projection of unity and consensus within the House of Saud and Wahhabi religious establishment to the outside world masked bitter internal divisions and power intrigues, especially, I argue, in the 1990s and early 2000s. Meanwhile, Osama bin Laden - with many ideological sympathizers within the Kingdom and across the Islamic world (though very few outright endorsed his tactics, let alone joined al-Qaeda or similar groups) - was escalating his rhetoric and his operational planning, leading to many plots, most of which failed; but a few obviously succeeded, including the biggest one of all on the American homeland.
I hope that makes sense.