> Otherwise a small country could just fine Apple $1T and solve its budget woes, and probably build a giant waterslide.
You're joining two things here which I think are important to keep separate--the demand and the enforcement.
The Province of Bumbinga can absolutely claim worldwide jurisdiction and fine Apple $1T. And they can fine them a further $1T for every day they're not paid and their waterslide is not built.
Hell, _I_ could send Apple a letter claiming they owe me a trillion dollars so I can build a waterslide.
But when Apple doesn't pay a trillion dollars... then what? Send them angry letters? Still doesn't get the waterslide built.
A legal system's power isn't the orders it's the enforcement mechanism behind it. With a local presence they have the option to seize local assets and bank accounts, forcefully close operations, arrest employees, etc.
When the company has no local presence, your only enforcement mechanism is gaining the cooperation of a foreign country, in which case the country they're headquartered in is very relevant. And they're only going to cooperate if your request aligns with their ideals and generally benefits them.
Except in the most extreme cases, it's generally not worth it to try and impose your rule outside your borders because you have no mechanism to make anyone comply. It's an empty threat. Jurisdiction in the international sense is descriptive not prescriptive. It's recognition of the limits of your authority. The outcome is the same with or without it.
Signal may have users in Sweden which Sweden sees as giving it jurisdiction. Sweden may see it being accessible at all as giving them jurisdiction. Sweden may say "screw it, we have jurisdiction over the whole world!". But their ability to enforce that more or less ends at requiring ISPs to block their traffic or asking the US government to enforce their orders within US borders, so it's kind of a moot point.