Why don't brakes come with 'Safety Levers' any more? It used to be very common to see bikes with dual pull brake levers (if that's even the right name) as shown below. However now it seems almost impossible to find brakes like this.  Even finding a picture to post was hard.  It seems like it would be quite useful to be able to brake from various hand positions.  There was an answer I read a while back (can't find it now) that stated that there was a reason they got rid of those, but no explanation as to why. So any technical reason, or is it just for looks?
I believe there are multiple reasons that "extension"/"dual-pull"/"safety"/"suicide" levers aren't seen anymore:


They're really a solution for a poorly fit bike, where the rider can't reach the regular brake levers. Fix that and you don't need an extra lever on the flat of the handlebars. This was especially a problem for smaller riders. Bike sizing and fit have improved a lot since then.
Since they effectively pre-pull your brake a little, they reduce how much travel you can get out of the primary brake lever which can reduce the effectiveness of that primary brake lever. (I guess some designs don't have this problem, but most did)
Using them puts your hands in a location that doesn't give you much leverage for controlling the bike.
It's an extra piece that can break (and leave you unable to brake). Especially, if the main brake lever is knocked out of alignment, the extension lever will hit the handlebar.
Modern brake levers ("aero"?) have a different pivot setup that works better over all, but especially works better with hands on the hoods than old levers did. Extension levers simply won't work because of the way a modern lever pivots. If you look at a modern brake lever, when you pull the lever the top of the lever doesn't go down, it goes forward, and extension levers rely on pushing down on the top of the lever. Sin As you can see from these blurry pictures of a vaguely modern brake lever, the pivot is somewhat low and in front and the top of the lever rotates straight forward.  
Somebody invented "interrupter" or "cyclocross" levers which go mid-cable instead, allowing you to get the same end result (a second brake lever) without any of the problems of extension levers.
Some regulation changes and historical market realities that ʍǝɥʇɐɯ discusses in his answer.