What's the problem that SSH tunneling is trying to solve?

Currently in my company, we're using VPN->Then RDP. And inside RDP, we access remote server. While some servers are directly accessible, some are not. We need to do tunneling for it. I'm failing to understand the point of tunneling. I've read articles after articles like this(https://www.gaia-gis.it/fossil/virtualpg/wiki?name=port-forwarding), but it's not entering my head. Can't anyone who knows the server IP and has company VPN; tunnel and get access to that server? I know they can, but what's the point of that tunnel? They could've just filtered by requests coming via a particular IP say xx.xx.xx.xx to be allowed and reject everything else. What's the point of tunneling?

What's the problem that tunneling is trying to solve