Short answer: Human Rights above the political affiliation.
Why
America’s commitment to human rights
Biden’s declaration represents an important step toward fulfilling America’s commitment to human rights across the world. At home, it begins to close the open wound at the center of the Armenian American experience. — Charlie Mahtesian at Politico
It is also a step that endorses the values of liberal democracy, by affirming core values such as the protection of human rights, justice and the protection of minorities against discrimination and violence. — Eldad Ben Aharon at Haaretz
Supporting the international institutions dedicated to those values:
It also boosts international institutions dedicated to those values, such as the InternalInternational Criminal Court and the UN’s Responsibility to Protect, a 2005 commitment to prevent genocide, war crimes, ethnic cleansing and crimes against humanity. — Eldad Ben Aharon at Haaretz
It was one of Biden's campaign promises:
On the campaign trail in 2019, Biden was at a Boston-area fundraiser hosted by Larry Lucchino, former Boston Red Sox president and CEO, when he saw Anthony Barsamian, co-chair of the Armenian Assembly of America, and reached out his hand.
“I know how important the Armenian Genocide is to you. Of course it’s genocide,” Biden said, according to Barsamian. “I didn’t even need to say anything. He led with that.” — Politico
Peer pressure:
On Wednesday, a bipartisan group of more than 100 House members also signed a letter to Biden calling on him to become the first U.S. president to formally recognize the atrocities as genocide. Democratic Rep. Adam Schiff of California spearheaded the letter.
"If we aren’t going to recognize a genocide that happened a century ago, what does that say about our willingness to stand up and confront a genocide happening today?" Schiff told FOX 11 Los Angeles. — Fox13 News
Why Not Earlier
President Obama declined to refer to the 1915 massacre of Armenians as genocide, breaking a campaign promise. 2015 was important as it was a 100's anniversary of this tragic event.
The Trump administration more relied on tit-for-tat relationship with the Erdogan administration. Even after the U.S. Congress in 2019 passed a bipartisan and almost unanimous 405-11 resolution calling the killings a genocide, after the furious reaction of Turkish President Erdogan, Trump officially rejected to supportsupporting the Senate.
My personal opinion, safe to skip.
One factor many people tend to mix here is the war in Karabakh.
Many of my Armenian friends and colleagues, after the world's almost unanimous support for Azerbaijan over the September 2020 events, were frustrated claiming that the international opinion was too much influenced by Turkey, rendering the unfair attitude toward the entire Armenian nation. It was hard (for me) to explain that the two events — 1915 and 2020 — are different by its nature and should be evaluated separately.
In my understanding, the Biden Administration has demonstrated that the two are different events, and each of these should be treated fairly from the position of Human Rights and human values.
