More to the point, Biden is not Obama. As an old, white man he does not inspire the same hope that Obama did in 2008.
Electing Biden as the Democratic candidate does not, and cannot, replicate the Obama administration. Additionally, Biden is not even endorsed by the former President.
Biden portrays a nostalgic idea of the Obama administration that does not actually exist. Post-Trump, Americans do not need "business as usual" from the Obama era; they need large scale change.
The Obama era failed to the make broad change that many voters see as necessary, such as introducing single-payer healthcare or adequate climate change legislation.