I don't it's an obsession with sliding per say - that's what Formula D is for
. Rather, it's a desire to see cars with enormous amounts of power with little grip - a recipe for an extremely difficult car to drive at the limit. You're correct that a modern racecar with downforce is slower when sliding, but with low grip, that's not always the case. If you look at F1 in the 50s and 60s, sliding the car through the corners with a 4-wheel drift was the fastest way through a corner. The poor grip of the front tires leads to understear, so you use trail braking and the throttle to enduce a slide, which helps rotate the car through the corner. It's much faster to do that as opposed to not touching the throttle, waiting for the front end to bite.