Actually, the Saudis can detect incoming drones or cruise missiles, assuming they had an AWACS airborne at the time. I’m quite sure that we did and know exactly what was used, by whom and from whence the attack was launched.
As to why the Saudis haven’t/won’t(?) respond, a significant number of officers in the Saudi military are “members of the royal family,” none of whom are in a hurry to die. I trained quite a few of their army officers and a couple of air force officers and I got the impression that they considered their military equipment their playthings and service in the military was an obligation of sorts, not something to be taken seriously (kind of like much of British royalty). Attacking essentially undefended targets in Yemen is one thing; flying into Iranian (Russian) air defense systems is quite another.
Why would Iran do this? Iran’s economy is collapsing. Whether it will result in the dissolution of the theocracy, we’ll see, but I doubt it. Like dictators everywhere, the mullahs know that the Iranian people - and not the mullahs - will be the ones to suffer.
Iran would conduct such an attack for a few reasons, all of which they’ve done before. Iran seized foreign vessels (not US) to demonstrate that they could and to remind people of the vulnerability and strategic importance of the Strait of Hormuz, knowing full well that there would be no military response - despite the fact that they committed an act of war. By so doing, they could increase international pressure on the US to lift sanctions. They conducted this attack for the very same reasons.
If they believed there would be no repercussions, then why do it at all? What’s their advantage? To let the world know what they already know? No disrespect but that doesn’t add up in my mind.
They must be playing a longer game here, thinking several moves ahead. OK, so trying to play devils advocate, if they really believed there would be no repercussions, then this move could be an attempt to show Trump/US as a paper tiger - afraid to engage in conflict. That could very well be a calculus of theirs. They think Trump won’t engage, won’t do much damage, or won’t make it to a second term. Enemies of the US in China, Iran, Russia and elsewhere would love to show Trump as an empty suit / naked emperor.
But I don’t think that is a proper evaluation of the man or the situation. I think Trump would be more than happy to give back to them as good as they gave. It plays into his ‘deal of the century’ to neuter Iran and the Iranian regime. It also plays into his plans to disengage, as ironic as that seems - but taking out the Iranian regime and pushing an Israeli-Arab peace deal is easier with Iran out of the picture. Maybe as you say the regime will survive but I don’t see why, if we engage, we should let the mullah’s save face. If we engage, they will fall by our hand or by the gallows of their own people for screwing it up. We’ll see who is right in due time of course. But I saw what we did in Kosovo, what we did during Gulf War I. Those were not the dragged out conflicts of Iraq/Afghanistan post 9/11. Those were shock and awe - 100 days of bombing. Potentially, without one boot in Iranian soil (or, just a small number to laser the targets I don’t know what the technology is today), we could cripple Iran and it’s political regime. Neither the Iranian economy, nor the regime, could last 100 days of sustained military attacks from the air and sea. I don’t see Russia stepping in the way - indeed Russia could be bought off imo with promises of future Iranian market deals.
And an attack on Iran opens the floodgates - Israel will move to crush Hamas. Israel/US will move to crush Hezbullah in Syria and the Syrian proxy armies. Maybe Assad will survive but he will be isolated without Iran or Hezbullah or Hamas. Iran is facing total political and economic annihilation. It’s one hell of a gambit - assuming of course they are behind the attacks. Whether they are behind the attack or not, someone wants to blame them for it.
It’s a sad state of affairs these days. Having observed what the “deep state” has done in the attempt to remove/marginalize Trump, it is hard - very hard - to take what they may say seriously. They supported Obama’s Iran deal. Now they support, perhaps, strikes on Iran? It’s too much to bear honestly. I don’t know whom to trust. Even if I give Trump 100% of the benefit of doubt I can’t be sure he isn’t being played. Friggin’ sucks, frankly.