Why do you expect that? Many DBMS operations that are not I/O limited are memory limited, and a GPU does not help you there (on the contrary, you get another bottleneck in data transfers to the small GPU memory). What can help is better data organization, e.g. transposed (columnar) storage.
The more complex the operations performed on the columns (trasnform), the better the GPU database will be - because of the higher ops/bytes ratio