I’m not an expert on squids, but I think it has to do with their soft bodies. They’re made of mostly liquid, whereas we need air to live, and air is very easily compressed under high pressure. The pressure outside of a squid will be about the same as inside, so they should be fine.
I did once read that suddenly bringing a squid to the surface will kill it though, because the high pressure of liquid in it will explode out into the air!
Humans would not explode! Gases can be compressed under pressure,but not liquids. Therefore, the gas in our body (ie in our lungs) would get compressed, so our lungs would shrink meaning they cannot work as well.
Scuba divers that come to the surface too quickly get something called the ‘bends’. If the pressure blood is put under changes too fast (by coming up to the surface quickly), the nitrogen in the blood turns in to a gas, creating tiny bubbles. These can make people really ill, as the bubbles can block tiny blood vessels. The solution is to come up slowly.
As Suzanne says, deep water creatures avoid these problems by not having gas inside them, but they get sick or die if they are bought to the surface.
Suzanne and Claire already answered the question but, just in case you’re not aware, I just want to add that squids are invertebrates, meaning they have no skeleton which is why their bodies can be so soft and they just compress rather than trying to hold the pressure.