Hmm, a few considerations on your points:
* Not being able to play with other servers: that's fine and expected, to be honest. Ping > more people to play, 100%.
* Enough population: maybe. I'd wager we do have enough population tbh. I mean, sure, Brazil doesn't have nearly as many people as US, but we're like top 6 or 7 in the world regarding pure amount of people. It's like 2/3 of US. Also, the other countries in SA have a considerable amount of people. Afaik, all the other countries together have more or less the same amount of people as Brazil, so we're looking at roughly half a billion people.
So, yeah, there's many other factors regarding how many of those people even has interest/are in age range, could know about Steam, etc.
Speaking in Steam terms, though, there are numbers indicating that Brazil has like 5% of all Steam users (vs ~15% of US). So if US has enough people to fill what? 30+ servers? Yeah, I'm pretty sure we can fill at least three.
* Language: Eh, not really. Most people that play MMOs don't really care, tbh. They either can read English or Spanish well enough to understand everything that matters in game. Spanish accounts for roughly half of SA population straight away, while the other half, in Brazil, can usually get by with Spanish if they don't know English, since the Portuguese and Spanish are very close.
Proof of this is that Lost Ark has launched in SA with no Portuguese, and has seen **massive** amounts of people on the servers. The "main two" were overloaded within hours, to the point of queues.