Why are dark energy and matter important at roughly the same cosmic epoch?
Matter dilutes as the effective universe expands, while a cosmological constant has a fixed energy density. Their relative importance therefore changes over time, making the epoch when they are comparable a distinct question from why the constant is small. OPH's fixed-capacity branch proposes a value for the effective cosmological constant; that alone does not determine the matter abundance, an observer's epoch or a probability for observing the crossover. A complete account would need those quantities from the same cosmological construction and a justified way to compare observer locations in it. The coincidence is thus a useful additional test. Reusing the horizon-capacity formula is not enough to claim it has been explained.
See also What is dark energy?, Why is the cosmological constant so small?, Why would a complete map of the world not tell me “I am here”?
Also in Chapter 33: Why Was Every Open Problem the Same Problem?, Chapter 35: What Is Anything Made Of?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 29: Why 1/137, and Why Is There a Limit to What the Universe Can Remember?watch a universe make its own particles