There is IPv4, it's an internet address that points to a specific computer, or at least it's supposed to. IPv4 supports up to 4294967296 addresses, which might seem like a lot until you realize how many devices are connected to the internet.
Almost the entire IPv4 range is full, and ISPs have resorted to letting 1 IP point to multiple computers also known as NAT. It's what your router does, and why your laptop and phone all connect to the internet using your routers' IP address.
Carrier Grade NAT takes it one step further and allows hundreds or more home networks to connect from a single IP address.
CGNAT kind of sucks because you can't run servers behind them because it doesn't know which of the hundreds of computer traffic has to go to.
IPv6 would solve this entire mess, but ISP's won't invest in it because they don't want to spend the money and just delay the inevitable until they have to.
True ELI5:
We ran out of signs for house numbers and instead of getting new ones we started giving everyone in a street the same house number