This is sad, but was to be expected. Geopolitically, Brazil is huge, and it's mostly because of Brazil that the Portuguese language is one of the top 5 most spoken languages in the world (+200 million native speakers, versus the roughly 12 million ones we have in Portugal -- which will be down to ~8 million by 2025, if the birth-to-mortality rate doesn't radically change), but GOG is a company and deals with revenue, income and market share. South America is supposedly a meager 3% of GOG's world market, and Brazil is an even smaller share of that already ridiculously small percentage. It's not viable for GOG to maintain a Brazilian domain and waste time and money on a market that just isn't there -- and probably never will be. Brazil has a lot of people, for sure, but it's also going through one of the roughest periods of its history, economically speaking, and most Brazilians who game on the PC will still buy games on Nuuvem or whatever's the cheapest option for them, instead of GOG. Because as soon as the big publishers forced GOG to drop worldwide "fair pricing" and take up a regional pricing model, GOG immediately stopped being a cheap option for Brazilian customers. Another thing to bear in mind is that South America, in general, and Brazil, in particular, have pretty... lenient laws concerning copyright, and it's not just a coincidence that Brazil is one of the countries in the world with the highest rate of piracy (alongside Russia, for different reasons), which means the probability of the ordinary Brazilian PC gamer being a pirate and not buying games on GOG, Steam, or any other digital distributor is extremely high.
The only viable "solution" for this, that I can think of, is if GOG launches a .pt domain and merges the Brazilian and Portuguese markets under the umbrella of a Portuguese (language) store. I say this because Portugal has a much bigger percentage of GOG market share than Brazil -- even though still pretty small, in the European scope of things. This still wouldn't address the price issues, and Brazilian customers would still end up having to pay a ridiculous expensive amount of money for their games, because of regional pricing and the downright absurd international video game distribution policies Brazil enforces. But at least you'd still have a working forum in Portuguese, a fully localized storefront, with gamecards and descriptions in Portuguese.
For the record, and let's make this crystal clear, GOG isn't "leaving" Brazil. Brazilians can still access GOG.com and purchase games like everyone else; the Brazilian GOG employees even made sure to state that Brazilians can still set the price to R$ (BRL) and that PT-BR GOG Support will continue to be a thing. All that's ending is the .br domain; a PT-BR storefront; PT-BR GOG forums; PT-BR game pages, descriptions and news. GOG isn't suddenly vanishing from Brazil, which is what this petition makes it sound like.