Is there any reason lean meats are easier to digest besides them having low fat? For example are the fibers that make up the tissues easier to break down in any way?
Lean meats have less fat than fatty meats, so, yes, they are easier to digest; I'm not aware of any other thing that would make lean meat easier to digest. But this alone does not tell anything about health benefits of lean meat. For example, foods high in complex carbohydrates, which also contain dietary fiber (undigestible carbohydrates) are harder to digest than simple carbohydrates, like sugar, but are considered more beneficial for health (kumc.edu).
"Fiber" in meat is different than fiber in plant foods and refers to connective tissue, which is made mainly of collagen, which is a protein, which is harder to digest than the protein from muscle (PubMed). But it is not collagen fiber that makes meat lean; collagen fiber can be present in both lean and fatty meats.