And it's kinda my whole point: code that can only be consumed wholesale as shipped might technically be open source, but if backporting fixes to a year old version is nigh on impossible, is it truly open source in practice?
Debian has a release model for a reason and it's their raison d'etre. Of course they don't want to compromise that.
Considering the amount of other distros that use them as a base they're providing something that people want.