Public access systems used to be a bit more common, with perhaps the best example being sdf.lonestar.org (unix, iirc, not linux). In those days, with running Unix-like systems on the desktop (which Linux was more of at the time than it is lately what with some..."upgrades") being difficult due to hardware incompatibility (particularly winmodems), servers like sdf were a way to expose people who may otherwise not have any access to a unix environment. They were a useful collaboration platform for coding. Sure, you have chat optionality (with tools like the the "talk" program), but also bulletin boards, and file storage space (a few mb at the time) to collaborate in, and also typically a web host directory (sdf.lonestar.org/~user). Paid users could get things like background processes, which were particularly popular for running eggdrop bots or BNC servers.
These days, I do wonder a bit about what the use case really is. Just about all of this functionality exists either in web based form, or, if nothing else, you can literally spin up a free AWS VPS to accomplish the basics (or just, you know, plug in a raspberry pi). But, the barrier to access is low, and if you're a kid just dabbling into different operating systems and programming and all you have at home is a windows system, it's a lot quicker to fire up SSH than it is even to download and spin up a VM to see what the fuss is about. You may not stay long, but it may be the difference between trying something and not.
These days, I do wonder a bit about what the use case really is. Just about all of this functionality exists either in web based form, or, if nothing else, you can literally spin up a free AWS VPS to accomplish the basics (or just, you know, plug in a raspberry pi). But, the barrier to access is low, and if you're a kid just dabbling into different operating systems and programming and all you have at home is a windows system, it's a lot quicker to fire up SSH than it is even to download and spin up a VM to see what the fuss is about. You may not stay long, but it may be the difference between trying something and not.