Back in the day.... probably a few years before I was being born -- a strange craze swept cycling.  People were taking perfectly good arts and drilling holes in them. 

The idea was to save some weight -- but also create a pleasing design in the process.  Some guys did professional quality work, but many more were the shop employees or racers or just plain garage mechanics who tinkered.

Some drillium made enough of an impact that mass-produced parts started being sold with the holes already in them (of course, even back then, liability was an apparent concern; I've read that the holy parts weighed more than the unholed ones, indicating they were probably beefed up first, which sort of defeated the "hole"  purpose.  Be that as it may, however, note that the Campagnolo Nuovo Record brake levers were undrilled from the factory.  Super Record, which came later, had factory-drilled levers.

In short, drillium was big enough to influence the industry.  Even today, the popularity of drilled parts among "retro" riders enables companies like Velo Orange to offer "drillium" chainrings and cranks.  Of course, this is a niche market.  The truth is, Drillium hasn't been big for years.  Why?  One might as well ponder the nature of gravity.  Some say excessively drilled parts broke; others that as Super Record supplanted Nuovo Record there was less market for drilling; and of course, then parts started being made of carbon and stuff and this trend passed into history.

Sort of.

The truth is, there is always someone out there who tinkers.  I did this back in the 1990s to the shift levers on my old Gitane, because they were old enough to be "period" and i wanted to see how to do it, but except for the odd chainring, or sometimes chainrings made into home-made bash guards fro mountain bike use, those Suntour shift levers were all I ever drilled out before.  So after stumbling on some pics onlien that remonded me of my long-deceased Gitane, I decided to follow in the footsteps of the 70's, and drilled out a pair of dia-compe brakes.  Not bad, so I did the 105 group on my Trek 470... front and rear derailliuers, downtube shifters, brakes, and lastly, the brake levers.  My friend who runs a bike shop told me brake levers are hard to do and in the olden days guys built special jigs.  I did it freehand with a cordless drill while listening to oldies radio.

Now... if only I had more parts to practice on...!