Sweden is very bureaucratic and relying heavily on their domestic identification systems which are notoriously impossible to navigate for foreigners.
However it is of absolute necessity to get this part sorted out in order to make any kind of communication with the government in Sweden, so it boggles my mind if anyone didn't have access to the application long beforehand, if they've been living in Sweden for longer than a few months at most.
Age is no excuse. You simply cannot exist in Sweden without it.
The proces was then to apply for permanent residence using the offered agreement between UK and EU, by logging in, filling out the form and attaching the requested documents as proof of residence, and also the required biometric registration.
Sure, it wasn't easy, but it is going to be even more difficult afterwards. Anyone who is entering Sweden (from outside EU) after this, will have to apply to the ordinary migration system which includes a test in both language and history of Sweden.