Of course they do, but a lot of people are behind CGNAT and do not have a public IP address assigned to their CPE, and as such reaching a device in the LAN from the outside - without the device reaching out to you first - is impossible.
And, of course, it can't reach out to your phone because it's also behind CGNAT. So, you need a VPS to act as a bridge between your phone and the device, which would connect to the VPS on boot and route traffic through a tunnel.
And, of course, it can't reach out to your phone because it's also behind CGNAT. So, you need a VPS to act as a bridge between your phone and the device, which would connect to the VPS on boot and route traffic through a tunnel.