The EU has 27 member countries, only 19 of which use the Euro; maintaining a sovereign currency doesn't seem to be a 'special deal'.
They are required to adopt the Euro, as soon as they fulfill the Convergence criteria Those convergence criteria include "Compatibility of legislation", and Sweden simply doesn't make their laws compatible. (Details here: https://ec.europa.eu/info/sites/default/files/economy-financ...)
In summary, they have to join, if they are compliant. For that they have to pass laws, and they chose not to. So, it isn't quite as mandatory as some people paint it.
To quote from the report:
> The Swedish authorities are invited to remedy the abovementioned incompatibilities