AIUI, and note I am better versed in chemistry/physics than biology/biochem, while epigenetics is not totally divorced from genetics, it is often something that arises from things like previously non-coding genes, from modifications of how a section of genome is expressed* which are themselves not actually directed by the genome,
I did a whole speech about this in HS. TL;DR: Imagine a gene has five blocks, ABCDE. In the past, we thought that was all there was to a gene, it has a start codon and a stop codon and you get those five sections in that order. However, complex organisms (and humans show this to a greater degree than any other form of life on Earth, IIRC) can start late and make protein BCDE or even CDE, stop early (making ABCD/ABC), both of those (BCD), or skip one or more internal sections (ACDE, ABDE, ABCE, ACE, etc.).
That means a single section of coding DNA may actually code for a dozen or more different proteins, all of which can do radically different things, and which one actually happens depends on the general cell chemistry, not just the other expressed genes. And all of that isn't even considering the impact of stuff that can mitigate or suppress genes that are present and active, but which are defeasible by environmental impacts.
This stuff is hella complicated.