He wanted to give them the opportunity to redeem themselves through teshuva. He created a similar opportunity to prove that they did a full teshuva.
These great men knew their place in history – that they were creating a great nation. Yosef wanted the patriarch of each tribe to live in dignity, which will continue to their tribes. If he merely contacted Yaacov and forgave his brothers, they brothers would have lived out the rest of their lives with shame. Yosef removed that shame. The goal of building a great and proud was worth more to Yaacov than knowing about Yosef a few (nine really) years earlier