Pretty funny that bookies think it's more likely that Kamala Harris wins the 2024 election than Joe Biden winning a second term. Just goes to show the kind of expectation people have for his term!

I would have thought there'd be interest in bets for Mike Pence, but no one seemed willing to take the plunge on that one.
At near 78, Joe Biden is the oldest first term President ever elected, so it's no surprise that people are imagining he will either serve one term, or not see out the term for various reasons thus elevating Kamala Harris to the top job.
Take note the bets are for "elected" the next president, not assume office. Mike Pence could assume office for a few weeks if Trump walks out once the Electoral College votes are officially counted in a couple of weeks time.