Brazil's Covid rules are the same as ours (if not harsher eg not even accepting direct flights)...from gov.uk...
Aircraft passengers who have been in the UK, South Africa or India in the 14 days prior to arriving in Brazil must quarantine for 14 days.
Brazil has temporarily suspended all direct flights from or via the UK, and has temporarily suspended permission for foreigners who have been in the UK during the previous 14 days to board flights to Brazil. There are exemptions, including for resident foreigners, close family members of Brazilian nationals (partners/spouses, children, and parents/guardians), accredited government officials, and professionals working for international organisations. This exemption is subject to a requirement to quarantine on arrival in Brazil for 14 days. Some British nationals have been denied boarding by airlines. You should check with the airline before buying a ticket to confirm you will be allowed to board.
So, someone (or many people) are ignoring information that is clearly laid out, and then expect brick not to happen.
Basically a return trip would require 24 days of quarantine in total. 14 out 10 on return. Logistically, physically, professionally that can't happen and another solution is required. Which was available in the summer and CONMEBOL chose not to take.