They tend to require specific hardware like a NVIDIA GPU. As well as having an ever evolving large model file which they will want to frequently update. Some tools certainly have had offline versions but I guess not many people are interested in setting it all up and are happy with an instant web ui
You just need to code up your own model architecture and then train it on your data using some established ML framework. The first step is where well-chosen priors can make a real difference wrt. your end results.