Our customers don't want to spend vast amounts of time qualifying an entire new release when they can accept an isolated fix instead and do more focused testing. They might need the fix for some critical part of their product. If I was them I'd do the same - if the rest ain't broke, why risk fixing it?
If the qualifying process is long and expensive, doing a one-off fix does seem more logical. This is assuming you can be sure the fix really is isolated.
I do feel like a lot of companies over-exaggerate the need for multiple supported releases.
