IPv4 is 32 bits. It has a hard cap of ~4 billion addresses. China and India alone have 2.85 billion people.
Add in the United States and Europe, and now nobody else gets an IP address. South America, Canada, Mexico, Australia, Africa, the middle east, the rest of Southeast Asia, etc. don't get to use the internet. That's 4 billion people who don't get to use the internet.