One way out is to assume that the vacuum-energy vastly weakens over time and is not constant as imagined by Einstein. Under that hypothesis, the field was created in the early moments of the universe along with the other forces in nature, and now stretches across the universe like a spider web. As the universe expanded and cooled, gravity and quintessence were locked in an arm wrestle for dominance over space. Both fields weakened with the universe's expansion. But ultimately quintessence won out over gravity and took control to push galaxies apart.
Dark energy is just a basic feature of the universe.
Trying to explain it is as pointless as trying to explain why Earth was the right distance from the Sun for life to develop. Historically, successful scientific theories are assembled from the simplest ideas. Maybe gravity weakens over time. Astronomers plan to look at more distant supernovae to precisely track how the universe's expansion rate has changed, and this hopefully will narrow the dark energy alternatives. One of our goals is to test for dark energy and see if this is preposterous because we are just dead wrong, or find out that we really do live in a preposterous universe.