1) GPU development requires specific developer experience. Making performant GPU code is an even nastier and less intuitive problem than making performant CPU code. A naive implementation would be shockingly inefficient.
2) Leasing GPU hardware in a datacenter is very rare. You'd have to do it at the office, or build your own servers and install them yourself at a colo. Lots of time and effort.
Even if the GPU solution was 10x faster (it could be much more, but it depends on how much the CPU, disk, network is a bottleneck), if you're talking about reducing $50k in computer time to $5k in computer time, it's almost certainly not worth it. If you're talking about $2m to $200k, that's a completely different matter.