Decompression chamber for you, buddy

One thing I don’t understand about crew aboard submercibles is why they need to go in to decompression chambers upon their resurfacing? Well I DO know that it’s because while they were under, the weight of the water makes the air pressure within the craft increase, and they need to slowly “decompress” when they come back up in order to avoid the “bends”.

My question is, why can’t they make submercibles that maintain surface air pressure within the confines of the submercible? Is this a tall order? I understand this would put huge strain on the outside of the craft, but surely technology is getting to the point where we can build super-strength materials capable of withstanding such forces?

subs use normal air pressure. I think some submersibles going to really deep depths do use higher air pressure to relieve some strain on ht ehull allowing a deeper dive (which puts the strain back on)

My wag is if they build a craft capable of withstanding the pressure, you can always add more internal pressure and take it deeper.

Also, submercibles that have a moon-pool must be pressurized, lest the water flood the craft and compress all the air. Typical submarines don’t have moon pools, of course, so this isn’t important.