I suspect that some of it is incompetence, and some of it is the fact that there isn't a single 'they' here. For small orgs, or super-regimented big ones, there is indeed a single Ministry Of Central Procurement through which all external commerce flows. When that isn't the case, purchasing is usually a patchwork of confused individuals with budgets tied to specific things buying stuff in scattered tiny lots.
Yep, and Software Vendors are experts at identifying who in that patchwork has purchasing authority and what their procurement limits are. They will craft their software sale to stay within certain limits in order to avoid the next level of procurement approval.