For what it is worth, here is my opinion on dark energy and why the universe is expanding at a accelerating rate and not at a decreasing rate.
Scientists think that dark energy acts as a sort of vacuum energy.
So what i think is that there is more dark energy outside the universe than inside the universe and that would also explain the accelerating expansion of our universe.
Ps: this is just my observation from reading some articles about dark energy and to me it sounds very logical
