Alright, I was talking about the content of the containers, you are talking about the containers themselves. Given that the content is far more likely to be hazardous to the environment than a steel box (the worst part about it would be the paint and lubrication of the hinges - the rest can just harmlessly rust away), there's a reason for why I ignored the containers altogether.

To entertain what you're suggesting: 1,480 containers are lost on average per year. Let that one sink (in) for a minute. To the oceans, this really doesn't matter given how massive they are, but recovering even a handful of them would be a logistical nightmare. Those cute salvage bags you linked to can lift loads far in excess of your average shipping container - but not at average ocean depths: Most are meant for depths of no more than 50 meters, because that's the limit for most divers, which you need to attach these things to whatever you're trying to lift up. Those things you linked to aren't even rated for that, they are pretty much limited to surface use. Deep sea diving is a thing, of course, but first of all these guys are busy elsewhere (oil rigs, underwater cables, military divers, you name it) and they could not operate at the depths most containers are lying at either. The other issue is the pressure that needs to be overcome. Imagine the kind of equipment necessary to inflate something that deep underwater. Imagine making that kind of equipment work reliably (or at all) underwater. You'd have an easier time building equipment for space. Since I'm not in the biz, I've only ever heard of one company in the entire world that has a solution that can lift heavy equipment at these depths, which they used to bring a large piece of the Titanic up. The US Navy has a fancy crane (FADOSS) that would perhaps be more practical for this, but I would assume it's being kept in reserve for when the next Russian or Chinese military sub sinks in international waters.

Which brings us to the real issue: Even with all of the insurance money in the world, you can't just materialize a hundred or more submarines or deep sea cranes and the highly specialized crews and ships to operate them for this kind of operation, talent that is such high demand, it would be immediately snagged up for much more worthwhile scientific, commercial and "other" endeavors.

Granted, all of this is a very uneducated opinion by someone who has surface (heh) level knowledge of a billion things and more in-depth (third unintentional pun) knowledge of only a tiny fraction of that, but still. I love the thought experiment nature of this discussion though.