“Today shalt thou be with me in Paradise.” No way station along the way. Instead, a thief, like all Christian believers filled with sin, is cleansed.
“Paradise” as spoken of by Christ on the Cross to the Good Thief was not heaven. That would have put the good thief in heaven before Christ — because Christ was in the tomb for three days.
Have not you read the verses where the dead arose from their graves and roamed around Jerusalem, visible to only the believers?
They, too, were waiting for Christ to be the first to enter heaven.
Thus, paradise was a waiting place, a purifying place, as is Purgatory.
When a person is in Purgatory they know they will reach heaven, but they must undergo the waiting and purification for the sins against others and the harm those sins did. Sort of a reparation.