Different times. It used to be that while the two parties differed on how to get things done, they generally had the same goals. The Democrats and Republicans might argue fiercely on the best way to provide public education for example, but they both voted for things they thought would make education better. Both parties recognized that in order to legislate, both sides would have to negotiate and compromise. Sometimes your side did much better than the other one, sometimes not.
Then 2006 happened.
In 2006 the Democrats took control of the U.S. Congress for the first time since 1994. This meant that a lot of the Republicans that were used to compromising were kicked out of office. In 2009 after the Democrats also took control of the Executive branch, the Tea Party, a conservative political movement within the Republican party, rose with the intention of getting the party back in power with candidates that were further right than what had been there before. They were successful in 2010 following the passage of the Affordable Care Act and the new, younger Congresspeople were less willing to negotiate or compromise on anything. Their main method of legislating was to automatically oppose whatever President Obama supported. The Tea Party worked hard to push the Republican Party away from moderation and spent a lot of time and money to replace established politicians with newer, more conservative people.
This eventually led to the 2016 election, where even if Donald Trump had lost the primary election, the winner would still have been a hard right executive unwilling to meet Democrat priorities. This had the effect of seeing formerly moderate liberals get rebuffed over and over when it came to trying to meet in the middle and pass truly bipartisan bills. So what happened to the Republican party happened to the Democrats. More hard left individuals were elected and their supporters no longer want moderate stances or compromise because they don't see reciprocity from the Republicans.
Joe Biden is a product from an older, bygone era. He was necessary to win the general election away from Trump, but within his own party he isn't liberal enough to make the growing numbers of more extreme politicians and constituents happy.