When will the two largest providers of secure encrypted email make it the default for messages sent between them to be securely encrypted? If even they can't manage it what hope is there for the rest of the email world?
Places with firewalls just restrictive enough to be annoying like that sometimes try to block well-known VPN providers as well, so you may need to use a less common one or set up your own proxy if Tor isn't good enough. One simpler way if all you want to do is connect to those few specific servers is to use ssh port forwarding, if you happen to have a shell account somewhere (the use of wget suggests it might be not too unlikely.)
Given that it's easily circumvented as you've found, I don't think there's any legit security reason for institutions to block things like that, but they usually don't put much thought into it and it seems to happen pretty often. It's only if they lock things down more tightly that it'd do anything arguably useful, which would presumably be more obvsiously incompatible with their mission in the case of a public library.
Then again, maybe something else is going on because they haven't blocked the port completely: It does connect before getting that error.
Why would a library block non-standard destination ports? …Circumventions… (fedia.io)
There are two ways to get online at the library:...