Then there is the fact that Biden is not very good at campaigning. He’s infamously gaffe-prone — which made for an amusing contrast with the preternaturally-controlled Obama, but is also a big part of why both his previous campaigns for president flamed out almost immediately.
Biden currently enjoys the glow from the Obama era, which for all its major flaws was at least not nearly as bad as what we are experiencing under Trump. But if he becomes an official contender, candidates from all sides are going to tear into his hide. Opposition researchers are going to dig up whatever they can find on his personal foibles, and his Democratic competitors are going to savage his record on the war on crime and Wall Street. Elizabeth Warren in particular is guaranteed to attack him over the bankruptcy bill, which she correctly predicted at the time was going to be a disaster.
It’s not going to be pretty. If I were him, I’d sit back and enjoy the most comfortable retirement that could possibly be imagined.