As addresses started running out, the NAT RFC was published in 1994 and described NAT as a "short-term solution". NAT was never meant to be an integral part of IPv4. https://www.rfc-editor.org/rfc/rfc1631
NAT broke a ton of things which required more and more hacks piled on, making it more complex to build services on top if it (e.g., a server in the middle to proxy all the traffic needed between peers is a 100% requirement, with all the maintenance and scaling headaches that come with it).
If an address is not public how can you start an connection from it, or end a connection at it? A web server needs a public address if you want to have people reach it. And you, at some point, also have to have a public address if you want to connect to pubic services: either on your end-host, at your CPE/router's WAN interface, or on an interface of your ISP's CG-NAT box.
But having a public address on your end-host also allows for much more functionality than if you were stuck behind CPE-NAT or CG-NAT. Now, you don't have to use this functionality—just like how I didn't when my printer gets an publicly addressable (but not publicly reachable) IPv6 address—but it opens up various possibilities.
On top of that, it lulls you into a false sense of security, so you confidently think it's protecting you even when it isn't. At least not having NAT makes the actual state of your network clearer.
Yeah that's called port forwarding. It is like complaining that light is coming into your house through windows. Fully intentional.
If no other aspect of your setup blocks the connection, it'll be successful. If you were deploying NAT because you thought it would function as a firewall then this part is probably not intentional.
"Yeah? Well, you know, that's just like uh, your opinion, man." — The Dude
Publicly addressable ≠ publicly reachable.
When I was with my last ISP which had IPv6, my printer had a public address, but the only people who could reach it were those on my home network.