I raised the same question as asked by the OP several years ago. Both at an Ilford tour and on APUG.
To use a quote from the famous parable: "The seed fell on stony ground" in both cases. The plain fact is that most users of film use 35mm which is a 2:3 ratio and most users settle on 5x7 prints, being a good compromise between the slightly too small 6x4 prints and the very much too big and expensive 8x10 or even 6x8 for all 36 frames.
It has never been clear to me why none of the print paper manufacturers have moved to 5x7.5. Yes I know that not all formats(645, 6x6, 67) lend their negs to a 2:3 ratio but 35mm does.
However it is clear from the posts that we are relaxed, resigned etc about paper not meeting the 2:3 ratio so why should the manufacturers change?
It kind of backs up the lack of response my same question got from Ilford. They knew there was no groundswell for change. Yes there is a good deal of history surrounding print sizes and it would be troublesome to change and if we can live with things as they are then why change?
There are always good reasons why we shouldn't change and there is comfort in leaving things as they are even if they cannot be justified logically
However on balance I am glad that we didn't take the same attitude to the debate on the continuation of witch burning
pentaxuser