Because the Venezuelan government will hit them as hard as it can at large cost to its citizens.
In Panama’s case, that is pretty hard indeed. Venezuela importers owe exporters in the Colón Free Zone (CFZ) about $1.2 billion. That is to say, CFZ companies have already sold goods to companies in the Bolivarian Republic and are awaiting payment. In retaliation for voting with the U.S. and Canada at the OAS, the Venezuelan foreign minister now says that the Panamanian companies won’t be paid.
To make matters worse, Copa Airlines has $487 million locked up in Venezuela which the government won’t let them take out of the country.
Add it up and you have about 3% of Panama’s GDP. Now, the companies that are being hit will probably be able to finance the losses, so there likely won’t be much spillover to the broader economy. But it is a nasty punch in the nose. Now, it’s also one that hurts Venezuela quite a bit worse, but that’s likely the point. Caracas is demonstrating that it is not to be trifled with.
In that kind of situation, why bother to make noise? Nothing to gain, something to lose.
UPDATE: Yesterday President Maduro spoke out about the dispute. First, he sort of walked back the default, saying “The debt owned to Panamanian businesspeople will be paid without intermediaries.” Except that really makes very little sense. Unless they advanced credit for their goods, this proposal would mean paying twice whomever sold the goods to the CFZ businesses that sold them to Venezuelan customers. It would also be a bit of an investigatory nightmare. Moreover, the Venezuelan government keeps implausibly claiming that 90% of the goods were never delivered, which sort of puts a damper on their credibility.
What it really fun, however, is how Maduro then took a personal stab at President Martinelli. “He will be a fugitive from justice when he leaves the presidency. He’s involved in all the fishiness. He was into some abnormal dealings with the Canal expansion and will certainly go to jail.”