However, software engineering is not such a job. A cover letter showcasing a software engineer's ability to author vaguely reality-flavored prose and get past the HR drone doing the reading is not showcasing their ability to perform critical job functions to address business needs. Such an engineer is spending significant amounts of their time to tick a prediction-value-free box on someone else's ill-informed list.
I've literally never had a good experience with a company that wanted a cover letter. I've done it dozens of times. In every single case, with precisely zero exceptions, it's produced no value for me. I've been on the other end of hiring processes as well, and there I've similarly found precisely zero value in cover letters across dozens of cases. Fact-dense and fluff-light resumes are much more valuable.
Code samples? Great! Toy problems? Great! Prose? Not so great.
Do you need help solving the problem you appear to have where you may be misevaluating candidates by measuring them wrong? I have some ideas! It could be costing you the best candidates!