Pretty sure one of their main reasons for giving it to Obama was the Iran deal.
I doubt that since the Iran deal was reached six years later. They actually gave no specific reason for Obama's award, which isn't surprising given he'd only been in office 9 months.
Sorry I mixed up the year he got it, but here is their reasoning.
"The Norwegian Nobel Committee announced the award on October 9, 2009, citing Obama's promotion of nuclear nonproliferation and a "new climate" in international relations fostered by Obama, especially in reaching out to the Muslim world."
Not sure if he deserved it though.
Also another reason for Trump not to get the peace prize could be his handling of Iran which so far has been heavily criticized and lead to renewed hostilities.