The reason? Because his political views are too right-wing!
Aumann is a supporter of the basic human rights of Jews to live in Judea and Samaria, and he is against dividing Jerusalem.
The committee discussing who to give honorary degrees to considered Aumann but rejected him because his political opinions "do not reflect the values of the university."
This apparently puts him beyond the pale from the progressive Haifa University leadership who have no problem inviting anti-Israel activists to speak on campus. It has also granted honorary degrees to far left activists like Shulamit Aloni, who defended Jimmy Carter calling Israel an "apartheid" state. At the time the university praised her for having "values entrenched in the University of Haifa ethos."
The University has also banned playing Israel's national anthem at its law school graduation ceremony, presumably because it mentions that Israel is a Jewish state.
The "big tent" we hear so much about apparently only has a door open to the Left.
(h/t Steven Plaut)