Answer: It’s the teams pushing the wording of the rules as far as they can go, trying to make an aero advantage from the nose rules intended to make the sport safer. Although, it’s fair to say that the thumb shaped noses are as safe, as the more rounded ones raced by Mercedes.
Back in the days before eighties, F1 cars had not frontal crash protection, aside from perhaps a radiator, wing or fiberglass nose cone. As drivers were surviving the ensuing fires from crashes, the danger became leg injuries, so the sport enforced a frontal crash structure. At first this was just a rudimentary 20cm structure that wasn’t crash tested or made to any particular specification. This crash structure grew longer, and then the driver’s feet had to be behind the front axle line until the point that the nose was formally crash tested structure. So, with the ‘nose’ doing its job of preserving the driver legs in a crash, the emphasis switched to other accidents, it was found that nose to rear tyre contact would flip the following car upwards, as demonstrated by Mark Webber at Valencia one year! Equally the ever-rising nose tips of the mid-2000s meant that it was possible for the nose tip to be high than the cockpit side, so the nose could ride over the cockpit opening and strike the driver’s head, not a pleasant thought. But as demonstrated by the high nosed Tyrrell 016, a high nose creates an aerodynamic advantage so great, that the compromises in centre of gravity height and suspension geometry were worth the penalty. So, when the FIA tried to lower the front of the car, the teams cried that they wanted to keep the height in order to preserve the aero gains and not have to redesign the entire car’s aero philosophy. So, the compromise was a chassis as high as was allowed and only the nose tip would be lowered. This created the stepped noses of 2012 and the subsequent rewrite for 2014 created what I politely called the ‘finger’ nose, although other body part and ‘devices’ have had their names tagged to these noses.
The aim with the finger nose was to substantially lower the nose tip and enforce a minimum cross section to the tip (8,000mm2), team avoided a large low nose by extruding the ‘fist’ size tip back into a larger wedge shape nose mounted higher up.
Then the rewrite was a stricter crash test and a demand for not just the one minimum cross section, but two, separate by 100mm, the tip being 8,000mm2 and the other behind it 20,000mm2. All most of the teams did was to shrink the nose around these two cross sections and the long finger became more like a fat thumb. These are the rules we are left with today, although the 2017 regulations demand a longer nose overall, the airflow gains from the slimmest possible nose still reward the thumb tip. Although Mercedes have found success with a nose tip that rounds the two cross sections and merges them into a more pleasing streamlined tip. As it stands there isn’t a plan to reword the nose rules to clean up the thumb tips, so we will continue to see them on the cars this year.