Forced to resign means a sympathetic option for dismissal. (if the reason is disciplinary). If an employee is forced to resign due to excess staff or closing of the department or the institution etc.or similar reason then the case is different. But resignation does not permit giving a severance package if there is no provision for such in the contract of employment. If a package is negotiated and agreed in closure of a govt. business a severance package is normally included in the agreement.
Practices differ in different countries. (Jurisdictions). In a case of sympathetic option.. this is offered to give some relief because the loss of terminal benefits are too big a punishment.