First, let me say that I don't mind the occasional occasion where you can actually putt out of a bunker, even if I have never done it myself and that I don't generally feel it is the safest option....
However, after seing the bunkers of the links courses of Scotland for the first time last month, I'm starting to feel that most bunkers (at least, in North America) are way to easy to get out of. And that includes the occasional opportunity to putt out of a bunker.
IMHO, bunkers are mostly meant to be hazards, and you should stay away from hazards. Flirt with them as much as possible, but stay away from them if you don't want to suffer the conscequences.
I am so glad that we are starting to see more and more of natural looking bunkers that are deep with big thick lips framed with fescues and indigenous plants. These bunkers are not only more beautiful in my mind, but they are also create fear to some degree in the golfers mind (at least it works for me!).
So, make the bunkers more penal! Not easier.... Let's stop making bunkers the golfers aim for because they are so easy to get out of.... Let's use the fluffy sand, let's put fewer rakes around them, let's make them deeper, and bring back those big thick lips!
So, to answer the question, I don't think that architects build bunkers you can putt out of. I think they evolve like that. I don't personnaly think we should try to do it either.