1. The straight of Hormuz is crazy because of the sheer amount of options Iran has to threaten shipping. It's so narrow that they can even hit ships with artillery fire. No need for missiles or drones at all! Lobbing kinetic shells may sound primitive, but anti-missile defences are designed to deal with large projectiles with minutes or hours of warning, not shell-sized projectiles that hit within seconds. If a U.S. war-ship enters the straight, they could be struck by fire from artillery that's been concealed for decades before they know they're under fire. It's also worth noting that Shahad drones have a larger range than the size of Iran, and they're hidden all over the country. Any ship transiting Hormuz or any ground force trying to land in Iran could face drone attack from anywhere in Iran, or all of it simultaneously. A few drones are easy to intercept, but give Iran a juicy enough target and they could make the decision to simply overwhelm it. Drones are a heavily parallel capability.
2. There are only a couple of lanes deep enough for large ships in the straight. So far, no ships have been sunk outright, and that's probably a deliberate choice on Iran's part. If they sink a ship at the right spot, the straight could become barricaded. Clearing that barricade under threat of fire would be a far worse pickle than what we're seeing now.
3. The critical question to ask is, "How does the U.S. end this?" Just continuing to bomb Iran is phenomenally expensive and likely won't accomplish much. This is a regime that has been preparing for an American invasion since they overthrew the CIA-installed Shah 47 years ago. They probably never seriously expected to win an air-war against the U.S. and have obviously planned for an asymmetric conflict. The U.S. is not going to win this one without phenomenal amounts of blood, treasure, and will, but all of these are in short supply. A ground invasion of Iran would likely be worse than Afghanistan, Iraq, and Vietnam rolled into one. The U.S. can't win this war because they simply can't pay the price. Unfortunately, the straight of Hormuz gives Iran the ability to prevent Trump from simply TACO'ing out and proceeding to invade Cuba. Iran could keep the straight closed even after the U.S. withdraws their forces, and likely will to make sure everybody knows they can control the world economy at will. They're going to expect a peace settlement, and it won't be cheap.
4. This conflict lights a fire under the behinds of all nascent nuclear states. Iran would not have been invaded if they'd managed to build nuclear weapons. Even Iran is more likely to develop nuclear weapons now. Contrary to what some think, Iran isn't going to give up their enriched uranium and end their program just because the U.S. promises not to attack them again. Something like the JCPOA only works if some level of trust is possible, but Trump personally burned that. The best the U.S. is likely to get in negotiations is a superficial promise not to develop nuclear weapons, backed up by absolutely nothing. If the U.S. decides to end the program by force, the result will also be uncertain. Say the U.S. locates and extracts Iran's HEU from those underground facilities. How will they ever be certain they got it all without occupying the whole country?