This will be Biden's 2nd term if he wins and he has delivered no change of any real benefit in his 1st term so he is arguing from a different position than last time. He could beat Trump last time by saying "look how bad things are under Trump, I've got to be better than that" but this time he has to convince people that he is doing a good job and he isn't. He's not doing a terrible job or anything but he's not delivering any sort of real change. In a country where a lot of people aren't happy with the state of things the continuity argument is a difficult sell.
If you think Biden hasn't delivered any changes of real benefit, then perhaps you'd like to consider the info below.
Here's an abridged list of some of his accomplishments, taken from the even longer list in the linked article.
1. Passed a $1.2 trillion bipartisan infrastructure package.
2. Passed the first significant gun control legislation in 30 years.
3. Made a $369 billion investment in climate change, the largest in American history.
4. Provided $10,000 to $20,000 in college debt relief to Americans.
5. Cut child poverty in half through the American Rescue Plan.
6. Capped prescription drug prices at $2,000 per year for seniors.
7. Achieved historically low unemployment rates after the pandemic caused them to skyrocket.
8. Imposed a 15% minimum corporate tax on some of the largest corporations in the country.
9. Recommitted America to the global fight against climate change by rejoining the Paris Agreement.
10. Strengthened the NATO alliance in support of Ukraine after the Russian invasion.
11. Gave Medicare the power to negotiate lower prescription drug prices.
12. Created more jobs in one year (6.6 million) than any other president in U.S. history.
13. Reduced healthcare premiums under the Affordable Care Act by $800 a year.
14. Halted all federal executions after the previous administration reinstated them.
Biden's 23 greatest accomplishments