It's more who it was given to that in hindsight (though most people knew Souness was hardly a great manager) wasn't the best idea.
Shepherd went all-in on a pair of deuces and lost.
Oh, I am not condoning the appointment, far from it, but as NE5 says, Souness was their appointment, they obviously believed in him, so from that perspective it isn't exactly strange that they backed their man in a similar vain to other clubs who believe in their manager? They backed the wrong man, and the wrong man invested their backing badly, no doubt about that..