Mesh networks have some practical limits they are unlikely to overcome, like crossing an ocean, or any sufficiently large unpopulated area. You do need expensive dedicated infrastructure for that.
Nothing about that is a physical limitation of linking computers. That's a limitation of a specific type of linking computers. There is nothing that says people couldn't lay cable down on the Atlanitc to cross the pond. Nothing about that has to do with the concept of the network being made up of linked computers. That has everything to do with how they are linked.
