Why are few major cities located in the interior of Brazil between Atlantic ocean and Andes mountains?

The vast majority of Brazil's population lives along the Atlantic coast, and the interior of the country is sparsely populated. The main reasons for this are the Amazon rainforest and the terrain of the interior.

Amazon rainforest

The Amazon rainforest covers a large part of the interior of Brazil. The rainforest is very dense and difficult to navigate, making it difficult to build roads and other infrastructure. As a result, the interior of Brazil is relatively isolated from the rest of the country.

Terrain

In the interior, Brazil is also very mountainous. The mountains, coupled with the rainforest, made transportation difficult which hindered the development of larger cities.

Economy

Furthermore, much of the interior of the region has poor soil quality, which makes agriculture difficult and contributes to the sparse population of the interior.