I'm going to rain on the parade here...
You have three other problems that haven't been mentioned.
1. No matter how big you can make a cargo carrying submarine you could always make a cargo ship bigger. The submarine simply cannot carry the volume that a normal ship can hence it is only useful for highly valuable items. This limits it's usefulness because the ratio between value of cargo to operational costs of the vessel needs to be balanced to even make the operation financially worthwhile.
2. Underwater navigation isn't as easy as surface navigation and it you start making submarines larger to carry more cargo then you also make them easier to bump into things or get fouled in fishing nets etc. Even with the smaller submarines in service in most navies, there are plenty of accidents involving running into ships, fishing nets, underwater obstacles and even other subs.
Adding to that problem, gas leaks & fires on submarines are often much worse because of the enclosed environment.
More danger means more expense.
3. Crew; a submarine requires a crew that aren't necessarily 'better' than a surface ships crew but they need to be a lot more psychologically stable and prepared to do without some of the basics available to a surface ship - like how often they can shower, having to share sleeping quarters with two or three times what a surface ship does and so on.
There's a reason why nearly every submarine fleet in the world is made up of volunteer crew.
In cyberpunk, the cargo subs are owned by corporations who would typically use them for very high value cargoes - it simply would not be worth running a sub to carry a bunch of TVs (you could never carry enough to make it financially worth it - unless they're the worlds most expensive TVs). Most writers seem to like the cool factor of cargo submarines but forget the cost versus profit mentality that rules every corporation.
When a nation has used cargo subs, such as Germany in WW2, it has been for strategic materials, such as rubber & oil and the subs were being used as a way to break through any potential naval blockades. In other words, the national desire for the cargo was high enough to warrant the expense of transporting a relatively small cargo in a relatively expensive-to-run vessel.
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