If your wooden shield is hit with a ballistas bolt you don’t have to worry about repairing it because you are dead

If I just blocked a ballista bolt with my shield I don't care how much damage is taken.  You can keep the damn thing I'm done.

I saw a movie with 300 metal shields and 300 leather underwears.

bulletproof swat shields, and polyglass riot shields.

we are still using them today as we speak.

Trusty Patches is showing us his collection of shields.

Ounces make pounds, pounds make pain. Same reason we put plastic on fire arms whenever we get away with it.

I've read that the Norse (Vikings if you must) wanted shields that were thin enough to be penetrated so that opponents swords and axes would stick and become less usable. There are several eddaic examples of this usage, and old preserved medieval Swedish law codes describe how many shields were allowed to combatants dueing duels, i.e. they were considered highly expendable.

I really think it's a simple cost analysis. You can always find a carpenter or woodworker, even in a small village out in the middle of nowhere you're going to be able to find someone who can work with wood. If you're on campaign and building fortified camps, you've got access to engineers skilled with working with wood and plenty of wood to work with.

that larger shinny round metal one looks like the snow saucer we used to go sledding with

Hoplon isn’t a type of shield. It’s a general term for military equipment. The type of shield a classical hoplite carried was called an aspis.

I’d also consider that a blow coming in to a metal shield is likely to be deflected, and retain most of its energy wherever it ends up going, whereas with an organic shield will take some force out of it by getting damaged, and is more likely to bind the weapon and end the path of the blow in the shield. So the organic shield might give better protection against follow-through blows

Better question: Why would you use your finite steel supply to make 100 metal shields, when it could be used to make 2000 metal bosses for 2000 wooden shields? And when a wooden shield broke, the boss was usually fine, and so would be used in the construction of the new shield. That just exponentially better usage of a resource.

The answer to the question of why they don´t do more of this, usually is money

Certainly in the Anglo-Saxon and Viking peroid in North West Europe, the main source of iron was bog iron rather than iron ore. Metal was more expensive in that era than it was later.

Anyone that’s humped kit will tell you they don’t want anything made heavier.

I did have the thought watching this that many people equipped with metal shields in a formation might have an issue with projectiles NOT getting stuck. Like if it hits your shield, there's a pretty high chance it's either going down, towards your legs/feet, upwards towards your face or into the sky, and what goes up must come down, or towards the guys on your left and right.

Another advantage of bronze facing on a Hoplite shield is that it polishes well. In a culture with a strong emphasis on single combat, being big and shiny is imposing.

Having bronze faced shields was also a way for more affluent hoplites to show off their wealth.

The bronze facing on Greek aspides actually did contribute to their durability against spear thrusts, and was likely intended to do so. Reconstructive archaeologists have run tests in which they repeatedly struck un-faced and bronze covered replica shields with spears, and  they found that the glue holding together those without the facing tended to fail, producing splits and breaks in the shield. Those that did have the bronze layer, even though it was very thin, held together much better.

A bronze facing would certainly have made an aspis more resistant to missile weapons too, but those weren’t usually the main threat in Ancient Greek warfare, at least in the time period when the classic design emerged and thrived.  Most hoplites expected to fight other hoplites, primarily- missile exchanges might take place at the opening of a battle, but they tended to be rather desultory.  It was really only a major concern when fighting foreigners.

Oh, that might be an idea for "Arrows vs Armor", putting bronze sheathed and unsheathed shields versus arrows, slings, pila, and plumbata; including Greek vs Roman shields