There are 4 players in this war and they all have very different goals and "victory" conditions.

1. Israel wants to ruin Iran permanently, to turn it into Somalia 2.0, meaning a quasi-state with no organized, central government. Were they to succeed in this it would be a humantarian disaster the likes of which we haven't seen since probably WW2. Tens of millions of refugees that will probably collapse surrounding countries;

2. The US (IMHO) wanted to placate Israel with a cheap decapitation strike that would force regime change and bring in a US-friendly regime, similar to Venezuela. This was completely unrealistic and they completely underestimated Iran's ability to maintain an offensive capability. We don't even know how much Iran's missile and drone capability has been degraded (to the GP's point). I don't even believe it's been degraded 50% (as GP claimed) abut we have no way of knowing. The entire Iranian military is built to resist a strategic bombing campaign;

3. Iran no longer trusts the US as a good faith actor and negotiator after multiple incidents of acting in bad faith, killing their negotiators and bombing an embassy so their goal is to make the price of this war so high economically that the US never thinks about doing this ever again. And that's a cheap thing to do, as you note. Drones can close the Strait and ne devastating to the economies of the Gulf states; and

4. The Gulf States just want to maintain the pre-war status quo. Saudi Arabia in particular just wanted to contain Iran. They're less vulnerable to the Strait being closed but it's still a problem politically as the US and Israel are bombing other Muslims. The Gulf states are learning the the US security guarantee ain't worth shit but they can't break away from being US client states with their own unpopular regimes probably collapsing without US arms. But in a prolonged conflict some of them may collapse anyway, particularly Bahrain and even Iraq.

So Iran just fires a dozen ballistic missiles a day to remind Israel of the war Israel started. An estimated ~50% of missiles get through missile defences now. Otherwise threats and the occasional drone are sufficient to close the Strait and massively disrupt the ME3 airlines. Militarily, Iran can probably keep that up forever. Mobile missile launchers are cheap and drones can be launched from basically any truck. They're also produced and stored in underground basis that are essentially impervious to bombing short of nuclear weapons.

Many believed prior to Trump's speech this week that he would either escalate or pull out. Instead he found a secret third, worse option, which is to tell Europe and Asia "you're on your own" (with the Strait closure) after the US launched a war nobody but Israel wanted or supported. That's an interesting strategy because it's going to cause some serious soul-searching in all of these countries about the wisdom of US allegiance.