Since off-chain transactions are more and more common. Why would more bitcoin be needed by any entity if they can do all transactions using basically only one bitcoin and using the same channel?

Maybe I'm not understanding everything but let's say all the markets in the world started to use bitcoin in one single global market network. Couldn't they do all the transactions off-chain with only one earmarked bitcoin? What is the need for multiple bitcoins and other peoples bitcoin? In theory couldnt all transactions in the world be performed with only lets say one bitcoin?

please up vote if you also would want someone with some knowledge answering these questions, thank you