In our region it's very opportunistic. Those who go out deep into the forest to harvest timber, brazil nuts etc. spend months on end in the field. During that time it's most economical to collect everything you possibly can -- and that includes baby wild animals. These people are often hunting for bushmeat, but will specifically target mother animals (tapirs, spider monkeys etc) with young because they can eat the mother and take the baby to sell in Puerto Maldonado.
In other areas like Iquitos within the department of Loreto, wildlife trade and trafficking is more commercial. You can see wild animals and wildlife parts being sold in public markets. It's rampant. This is a whole other level of extraction, and why a lot of our seized animals come 2000 miles from Loreto to MDD to our center (like our baby jaguar Artemis).