It’s not surprising in the slightest due to the fundamentally flawed way the war prep was conducted.
There are, generally speaking, three kinds/categories of modern warfare. The first is the one the west has gotten accustomed to, where they can hit a hopelessly overmatched opponent from a position of absolute safety with minimal chances of losses and zero expectations of the enemy being able to hit even your major forward operating bases. In this kind of war, the attacking west holds all the cards and can decide how far to go and when to stop.
The second category of war is the one that we are seeing now, where opfor has genuine and sustained ability to hit back deep and hard. Where even major forward operating bases and carriers are not safe, which correspondingly massively limits and restricts western sortie generation rate, which is the heart and soul of western war fighting ability.
The third category of war is where you are fighting a true peer, if not outright superior force, that can not just damage your major assets and force concentration but decisively defeat them and potentially outright destroy them. Such a foe will also be able to take the fight right back to the west’s homelands without needing to go nuclear.
The fundamental strategic errors the US made in this war are hilariously many, but chief amongst them is the fact that America was preparing for entirely the wrong kind of fight, and not even doing the full prep needed for that. They thought it was going to be a Category 1 fight like with Iraq, where western air power could run rampant and dismantle Iranian war fighting ability and industrial capabilities systematically and quickly, but actually found themselves fighting a Category 2 war without all the tools and resources in theatre needed to fight at that level.
But as anyone with even cursory knowledge of history can tell you, during both Desert Storm and Iraqi Freedom, the US backed up and underpinnned its air power dominance with massive amounts of ground forces. Because even at the peak of its air power dominance, competent US commanders were cognisant of the limits of air power and knew that you needed boots on the ground to be able to both take full advantage of your own air power, as well as to force opfor into concentrating and revealing forces for your air power to hit.
Without the threat of ground forces, you see exactly the situation the US faces now, where the Iranians can disperse and hide their strengths so American air power is massively blunted, having all the fury but nowhere suitable to unleash it against. This is why they are bombing girls schools, universities and other soft civilian targets.
The US also realises this, but the problem is that they have already squandered the opportunity to build up and amass ground forces in peace before the commencement of combat operations, they cannot bring in army armoured divisions now as there is nowhere to land and base those forces now, not without receiving massive amounts of Iranian and local insurgent attacks, which will result in unacceptable levels of material and human losses before they can even get to the battlefield. Which is why they are now belatedly rushing in marines and airborne. But that’s an even worse option as you are throwing light infantry into the teeth of the enemy’s whole army with dubious supply lines, relying almost exclusively on air power for fire support, and with basically no fall back position or room for manoeuvre and limited evacuation options in the event it goes catastrophically wrong as they are setting it up for.
Let’s not forget that Iran has been holding back basically its entire anti ship arsenal. So there is a real chance the marines won’t even be able to make it alive to even hit the beaches in the first place. Or if the Iranians are really confident, they could allow the marines to land and then almost hold them hostage and trapped, obliging the USN to feed more and more ships into the slaughter in a doomed bit to resupply, reinforce and them exfil the amphibious forces. If the Iranians had any ASBMs or similar aces up their sleeves, that would also be perfect time to play them, because even damaging a carrier will basically doom the whole operating.
I think the key question now is whether the generals and admirals in the Pentagon can talk Trump down from this Epic Dumbass move, and what alternatives they could possibly fathom to turn this situation around.