It looks like OSRS has a large pool of premium VPN servers IP blocked from being able to access to their website and log-in to the game servers. I’d guess the free ones would be all blocked due to bot abuse, but it’s quite surprising for the paid ones to share the fate as well.
One good example is ProtonVPN, most of the premium servers are IP blocked on OSRS. I’m quite sure this isn’t only related to ProtonVPN, however. This is at least the case for WireGuard connections. Now around 1/4 of the servers remain unblocked, but it’s still an annoyance to find & pick the “right” one.
Now why is this an issue? Well some countries have restrictions on various content, and in some other countries there are ISPs not respecting net neutrality and throttling “unimportant” traffic (such as gaming). VPNs get around both of these cases.
Last, but not least, they protect the traffic (& passwords) from being intercepted if your PC is part of a larger network and they can be customised for malware & tracker blocking across all content the PC receives from the Internet (when browsing, etc.). They can boost your system’s security if used correctly.
All in all, I think these are solid arguments as to why somebody might opt for a VPN. Now the question is, can something be done about it from Jagex side to be less strict on VPNs?