I was thinking that and feeling rather proud of being European where we rarely use pre-mix (I've seen some in supermarkets but don't know anyone who uses them).
Then I realized that I typically buy my puff pre-made (made with butter) because it's good enough and it's hard to make at home... Most people I know do the same. Now granted, making puff pastry is quite a bit more involved than mixing ingredients like a pre-mix cookie recipe but still...
Puff pastry is also usually not the main part of whatever you're making but rather just something to hold it together. I see it more as buying pasta to go along my self-made stew - sure I could make it myself but for most dishes I wouldn't notice the difference. The cake mix is much more defining of the taste of the resulting cake so I'd want to have a say as to what goes into it instead of just using someone else's design.