Why is it hard to merge them? If they're doing the exact same thing, replacing with an abstracted function should be straightforward. If they're doing different

Why is it hard to merge them? If they're doing the exact same thing, replacing with an abstracted function should be straightforward. If they're doing different things, merging them may be unwise, since they may truly be different conceptually. On the other hand, I've definitely seen it become near impossible to unwind an abstraction once it starts getting used by other abstractions that are used in many other places in your code (multiply by as many levels or permutations as it takes to achieve desired level of complexity). Meanwhile, this poor function has been twisted to satisfy all these unreasonable demands from every corner of your codebase, and teasing it apart becomes an Herculean effort.