I read a wonderful article that went into this in some depth a while back but can't for the life of me recall where.
Basically, if you're doing some kind of NASA mars rover software, you go over it again and again and are really careful and all that costs a lot of money. It also means you have fewer features and it all takes longer. If you tried to use that sort of process on some banal bit of everyday software, it'd be way more expensive than the competition and have fewer features. You'd go out of business.
I also agree with the other commenters that quality hasn't really declined over the years.