You do, infact Super Trofeo Stradale, (aka STS road version), and Super Trofeo (GT3 race car) are both chassis mounted wings. The gallardo chassis actually has a top frame rail that makes it super easy and simple to do.
If you are talking about that whole trend with the huge wing uprights at the rear of the car, there is no benefit apart from looks.
mounting at the rear is disadvantageous for a bunch of reasons,
longer uprights are heavier, flex more, and tend to wobble a lot under corner loads
The uprights also act like a lever, rather than a compressive force directly downwards, the force tries to twist at the end of the chassis, it would produce more stress on the mounting points, so stronger and therefore heavier mounts are needed.
however there are a few early GT3 cars that did have these rear mounted wings, but it was not long before the switch went to top mounted wings... most likely just for simplicity.