In season 2 of The Flash, you meet Earth 2 Harrison Wells and his daughter Jessie. However, she has no E1 doppelganger.
2 Answers
Most probably because Eobard Thawne killed Harrison Wells too early and took over the identity that Harrison Wells got no chance to bear a child. Also, there is no Harrison Wells in earth 38 mentioned yet or Supergirl in earth 1 etc etc. So it seems every earth don't have the same person's doppelganger.
There probably isn't a Supergirl on earth 1 because Supergirl is originally from Krypton, so her doppelganger would be on Krypton in the Earth 1 universe, the same with Superman. Since doppelgangers tend to be different than each other they may have never come to earth 1 at all. I do agree with the idea that not everybody would have a doppelganger though, because if a person died before having children, like Earth 1 Wells, it would wipe out all of their possible descendants and this would be very unlikely to happen in every universe in the multiverse, leaving lots of people without doppelgangers.