I agree the best paper award should go to the paper with the strongest contributions, perhaps with writing quality as secondary. I don’t agree with your last sentence.

Writing quality is often a make or break thing when it comes to whether a paper is accepted or not, mostly because it makes a paper easier to understand, ie its contributions and the evidence that they are truly there are easy for a reviewer to pick up on and appreciate.

Furthermore a well written paper is a far larger contribution to the research community - the audience post reviewers - than a poorly written paper with the same contributions, for the same reasons: well written papers can be a joy to read, particularly if a leap in contributions are presented in an easy to understand way.

I understand that these things are cultural (ie field specific) but this has been my experience.

A badly written paper is bad at delivering its core content of scientific knowledge. The reading process less efficient, the understanding comes slower, and discussing the core ideas and findings is harder and less fruitful.

A well written paper transports the reader to the perspective of the writer. It’s not about poetry or aesthetics.

Bad handwriting is illegible. Good handwriting is clear. Calligraphic aesthetics is another domain.