My best bet is that they hope to attract BTC whales that need to liquidate some of their otherwise unspendable fortunes (I'm talking of wallets that on paper are worth billions of USD, but in practice are difficult to liquidate).
For example you could go there, buy a watch worth 100000 USD with Bitcoin, come back and resell it.
But I still find it hard to believe that would bring the Panamanian or Salvadorian jeweler any benefit, let alone the rest of the population. The problem of converting the BTC rests with them after the purchase.
There are already some countries that made a business of looking the other way when somebody wants to launder some money, that's been going on forever and isn't related to Bitcoin. The benefit to the population is that because the government gets to tax some part of the activity, the people's taxes are lower and the government can provide better services than it would otherwise. If this makes a country a kind of a tax haven, but for Bitcoin, then that's probably just business as usual, in a way (still wrong, though).
And even if it was, for many such store of value would still be difficult to liquidate compared to the average person. Let's just say that there are plenty of people that need to "clean" non trivial amounts of BTC
I bet dumping 1 or 2 USD billions worth of BTC each day would have a slight impact. Not to mention the fact that not everyone can sell noticeable amounts of BTC, let's say for "visibility" issues...
For example you could go there, buy a watch worth 100000 USD with Bitcoin, come back and resell it.