I see the possibility of several things going on. First, they do not appear to be planted correctly, although the mulch may be obscuring my view. They should be planted so the root flare - where the trunk widens out into the root system - is just above the soil line. 'Telephone poling' - or planting too deeply - can seriously shorten the life of the tree. Also the mulch is too close to the trunk - you want to keep mulch a proper distance away from the base of the tree, at least 3" all the way around.

The sudden wilting and the discolored wood exposed on the cut branch could be signs of a serious disease issue, Verticillium wilt. Maples are very prone to this soil borne pathogen and can react very suddenly, especially if they have been under stress for some reason (like poor planting methods). However, there are other pathogens that can create similar symptoms so your best bet is to have the trees looked at by a qualified arborist.