I think most everyone has the technical skills to go through this tutorial but a large chunk of the developing world will not be able to afford pcb manufacturing and all the tooling for SMD components.
Having an 8bit AVR with a through hole form factor democratizes access to electronics for a lot of people around the world.
Any maker can take a 1$ veroboard and build a semi-permanent circuit board with a very crude soldering iron. Whereas if you miniaturize further with SMD formats, then the access to materials and tools becomes an economic barrier.