Bitcoin uses a hashing algorithm called SHA256. This algorithm is easily implemented in hardware and is very parallelizeable. It's a simple pipeline with some adds, rotations, bit shifts, xors, etc. Once people started to build ASICs to mine Bitcoin, GPU mining simply wasn't competetive.

There are many other types of hashing algorithms, many of which aren't as easily pipeline-able. For instance, if a hashing algorithm requires a few megabytes of memory, than making a custom ASIC isn't going to have such a slam-dunk advantage over a GPU.