There's no coronation. If there was, Biden would have made a better showing in the early primary states. He didn't. He performed awfully. Yet no one else grabbed the nomination and, frankly, the African-American community then rallied hard behind Biden.
If a lifelong Republican or exhausted independent asks the question "why should I vote for Joe", then I respond with a statement and a question. "I don't know what your hot button issues are. Do you mind sharing with me?" If they share what they are, then I respond appropriately. But if all they want is a general response to "why should I vote for Joe?" then my answer is, "because, first and foremost, Joe Biden is a decent man. He has a nearly 5-decade long career of working with both Dems and the GOP on a wide range of issues. I'm guessing you voted for John McCain? Well, John McCain counted Joe as one of his best friends and John McCain intensely disliked the current POTUS. I'll also guess you voted for Mitt Romney? Mitt Romney voted to impeach the POTUS and is not going to vote for him in 2020. Loads of the current POTUS' former senior staff will not support him. 70-something former National Security officials, all Republican, signed a letter indicating why they will not vote for the POTUS in 2020 and will instead vote for Biden. This kind of rebuke from people who worked for the POTUS and served other Presidents of his same party is unprecedented. It speaks to the contrast. A decent, principled servant of the people versus someone who is noted as the opposite by his own people, his own party."
Glad you will be voting Biden!! If you want more talking points, feel free to DM. I'm doing what I can for a couple of hours every day via phone, text, chat, knocking on doors to make a difference. Hope you will join the effort. We need you.