What went wrong with my plum tree?

Hi, my 3 year old plum tree is no more. Admittedly I planted it in the wrong place, we're at the edge of a field and on top of a hill and the winds took care of most of the blossom. The 7 plums we so carefully nurtured were eventually got at by wasps etc and we've called it a day. The 8' tall tree looked very sick and sorry for itself. These are some of the roots. Is this normal? There were hard/solid lumps on them. Thanks :-)