Thats because many can't imagine Biden making it a full term let alone two terms. So his VP choice may very well have to step in as president during the 1st term and if Biden wins will almost certainly be the 2024 nominee. Which is why I'm so worried that he'll make a novelty Sarah Palin type pick by choosing Stacy Abrams instead of a solid credible pick like Kamala Harris, Susan Rice, or Tammy Duckworth. The latter is my hope though I don't expect it since she is the wrong skin color.