That one is easy. The universe is over 1/4 old.

Imagine streching a rubber-band beyond its limit. (Remember that a PERFECT vaccum would pull our universe against the force of gravity.)

At some point, the rubber band will BREAK. And when that happens what happens? The ends along with the whole thing, expannd faster in opposite directions exactly.

Expansion faster than gravity is not unnaceptable if we didn't know the first part of the equation - meaning the 1/4 of the timeline of the complete Universe.)

What I mean is that we have no way of knowing where half-way is.

Regardless of the theory, our Universe will cease to exist someday.

We know how old the universe is NOW, but we don't know how old it WILL be when it dies, so we can't know why we are expanding faster. We could still be in the first half of an explosion, or we could be at the end of a rubber band that snapped long after it passed the half-way mark.