When Democrats re-implement a 50-state strategy and having socially conservative and moderate office holders in the South and Plains is a priority for them.
I don't know where the idea that only conservative Democrats can win came from. Check out the ideology of the only Democratic Senator from Idaho in the last 60 years.
It's not really that they have to actually be conservative to win (I mean, no one would call Robert Byrd or Heuy Long conservative, would they?), but appearing socially conservative, IMO, gives a candidate more "folksy" credentials. Can you think of a type of politician who's more inherently populist-sounding than a socially conservative, fiscally liberal Democrat from a rural district?