Airplanes can't carry much in the way of sound supression or "mufflers" on engines. Running them on the ground, it should be straightforward to make them reasonably quiet.
The sheer volume of air moved by high pressure gas turbines makes that large and costly. Not impossible, but very large. These units are 2 per container size, intake and exhaust silencers would probably increase their footprint 5-8x. Not that it shouldn’t be done, just that there’s a lot of incentive not to do it.