You're right; if we look at sites like
https://bitnodes.io/ it is clear
BTC full nodes should be more decentralized, especially in developing countries.
Actually it is not clear at all from this picture. The only conclusion you can make here is that more
listening nodes are coming from those areas and when you check where they are you realize that most of them belong to data servers. In other words there is a lot of listening nodes on data servers.
Otherwise this site does not show all bitcoin nodes, majority of which don't listen for incoming connections.