I have a similar problem in this area. I chose GPU rendering, and every time I render the CPU is almost 100%, but the GPU does not work much.
Do you see such low GPU usage all the time? There are some operations during baking, such as UV unwrapping and lightmap de-nosing, that are always performed on CPU, so GPU will be idle during these operations.
I have two computer.
One One is 750Ti, and the other one is 1050Ti.
Windows’ Task Manager incorrectly reports the GPU load for baking. You can check the load in other tool, for instance GPU-Z Graphics Card GPU Information Utility - it should report 100% load.
The progress bar shows that the baking is at the ‘Denoising lightmaps’ step, which is always done fully on CPU.