The Hungarian Revolutionary Party of 1848 was essentially not a pure revolutionary party. Starting as a small faction of about a hundred and eighty people, it grew rapidly to become the leader of the Hungarian Republic, filled with too many opportunists.
It's easy to get on a boat but hard to get off. The Austrian Empire, which was on its last breath, was now fully revived, and the hearts of many were shattered.
If at this time, the Vienna Government issued a pardon, Budapest City would most likely surrender without a fight.
Clearly, this was impossible. Neither the Austrian Cabinet nor Franz, the Crown Prince, had any intention of passing up the opportunity to strike at the influential factions of Hungary.
Suppressing the rebellion was the perfect excuse to act. The wider the spread of the rebellion, the more Nobility involved, the more favorable it would be for Austria's future rule.