Why aren't these 2016 Democratic primary possibilities running for 2020?

[AltWorlder]

Actually ran:

• Martin O'Malley
• Jim Webb
• Lincoln Chafee
• Lawrence Lessig

Didn't run but were rumored:

https://en.wikipedia.org/wiki/2016_Democratic_Party_presidential_candidates#Potential_candidates_who_did_not_run

There's too many in that second list but the ones I'm most interested in (in terms of why they aren't running) are Russ Feingold, Al Gore, Christine Gregoire, Gary Locke, Adm. McRaven, Janet Napolitano, Jay Nixon, Kathleen Sebelius, Antonio Villaraigosa, and Tammy Baldwin.

Jerry Brown would be too old and some of those people are actually running this year.

[Roll Roons]

Feingold: Being a two-time loser probably doesn't look so good
Gore: He's been out of politics way too long and seems to be content with his climate change stuff
Gregoire and Locke: We already have Inslee. Do we really need multiple Washington governors in the race?
McRaven: Probably doesn't want to get into the meat grinder of the presidential race
Napolitano: Seems happy as UC president.
Nixon: His reputation was destroyed with his handling of Ferguson
Sebelius: Her tenure at HHS was pretty controversial...
Villaraigosa: Probably thought Garcetti would get in
Baldwin: Not sure. She'd be a good running mate for most of the male candidates.

[AltWorlder]

Awesome response post! I didn't actually expect someone would address all of the ones I was interested in.

Feel free to evaluate any of the folks from the first list of actual also-rans, or anybody else on the long lists in the link.

Come to think of it I wonder why Tim Kaine isn't running, if Edwards did in 2008.

[Progressive Pessimist]

Roll Roons pretty much nailed it. Honestly of all of those listed, Baldwin is the most relevant and probably just plain isn't interested in being President, I guess.

[AltWorlder]

I suppose Chafee did poorly in 2016 at the debates and isn't bothering this time.

Wonder why Webb isn't giving it a shot, since Ojeda backed out.