The guy edited his reply to this comment of yours with this:

EDIT - ah voltpower - didn't see your edit. If they have US product liability insurance and easy to reach tech support, we'd be happy to work on them.

It seems like product liability insurance is an issue, despite what some may want to believe.

https://www.reddit.com/r/ebike/comments/115b99j/this_is_why_we_wont_work_on_your/j91wam2/

To expand even further, many random ebike brands do not have the necessary product liability insurance for the US. This means if we change a flat or adjust your handlebars for you, and then something else fails and the rider is injured? Thats our fault, we are now held liable for the entire bike and you may not sue us... but your insurance company can and will.