Because I have never met a person who is great at that last part (methods theory) and sucks at the others (technical implementation; because the same work and effort leads one to train both). The issue is that AI solves all these problems at once, which will probably result in more academics understanding their methods and choices in preprocessing etc even less. At least this is what I have seen, and seen it getting worse.
I wish the problem was just finding the right packages. Web search, and mentoring/talking to colleagues are pretty good solutions to that. LLMs are more of a gamble here if one use them as an authoritative source, they may suggest the right package, or they may take you on a long trip to nowhere, depending on random factors.
In other words, relieving the researcher of the slog of editing proposals, figuring out compiler configuration, and locating esoteric code from years past they can be judged on the quality of their actual contribution now that the menial tasks can be delegated to an LLM and reviewed by hopefully the expert researcher.