Ray;
Even if you can get "quite good" imaging without masking, why not to implement masking in negative films because it is possible, and probably quite easy to do so? I think this is all about development. Many inventions are not groundbreaking, but fine-tune the results. Nothing is a "must", but today we take the extraordinarily high quality for granted, while it's mostly thanks to dozens of small inventions during decades.
With slides, if you added a mask, you would need a compensating blue filter in the projector so that orange mask + dye impurities + blue filter together equal to neutral density, but you would have huge light losses and it wouldn't be practical.
But orange mask in negative material, which is not to be viewed directly anyway, is very practical and is very easy to compensate for in all workflows. For example, RA-4 papers have different sensitivities for R/G/B emulsions so that orange light will work directly. (In fact it's made even more red-orange with the filtration, so the "mask" helps with this. This is because of color separation without the need of yellow filter layer in paper.)
However, orange mask has started causing some (usually minor) problems in the 2000's because of some scanners that are built by idiots, and software written by idiots. Luckily, we don't need to discuss this at APUG in detail which is why I love this place.
PE and Ray, please try to keep calm... I don't know what's going on with you two or why, but I know it doesn't make anyone feel good.