There is a large aircraft overhaul and maintanence facility called Mobile Aerospace Engineering,that does work on several large aircraft so may have been bringing engines or other equipment needed for one of the repairs.
The reason the AN-225 came was to bring in 2 large drill heads. The cargo was very urgent and there was no AN-124 or other suitable aircraft available in the short time frame available. So the 225 was called upon to do this job.
It may not be the weight but the size. They could be too big for an aircraft smaller than than the AN124 or AN225. Could also be other equipment going with the drills.
Welcome to the forum. If there are any more An-225 flights to the US, please drop us a line. I’m sure there will be a lot of grateful people at whatever airport it lands at.
I was looking for local news articles/pictures on him and found this site by accident although I do use the flight tracker to keep tabs on our aircarft when flying in the States.