Let's look at what happened. RFK Jr, a Dem his whole life, ran for the Dem nomination as POTUS. The DNC pulled every dirty trick in the book to thwart him until he finally took the hint and left and ran as an Independent instead. And he had a fair bit of success, especially considering the complete lack of MSM coverage except for the occasional hit piece. And he did it by taking on any interviewer that would talk to him, something Biden has never done in his 50 years in politics and that Harris doesn't do either.
After all that he finally decided to stop his POTUS run. And then he called the Dems to talk to them to see if they'd give some consideration of some the issues important to him in exchange for an endorsement, issues that obviously were important to a lot of other people too since he garnered a fair bit of support for an Independent POTUS candidate with no MSM coverage.
And they wouldn't even talk to him! What in the hell did they expect him to do after that? Just go away and do nothing? It's like they said "We can treat you like complete garbage the entire way, even up to the point where you have a lot of leverage because you have the support of a percentage of people that could be the deciding factor in a close race, and even then we'll continue to treat you like garbage." How unbelievably dumb of the Dems. All they had to do was give him a little bit and have RFK Jr endorse Biden in return and it'd have been game over.