I mean, if you're transporting literally tons of cocaine at a go in disposable microsubs, you think the best thing is to attract a lot of attention by (a) stealing a rich, and therefore politically connected, person's submarine that (b) is trivially tracked by the USN?

I mean, size isn't stealthy. And it's not necessary for cocaine. It's the same reason that they smuggled coke on private planes instead of hihacking 747s.