It doesn't need to be that complicated, but unfortunately, it was in that case. Logistics and downtime control created an environment where central purchasing was not a requirement - many of the field teams, especially in remote locations, would go to various online subscription-only telecom equipment swap-and-shop sites to ensure a constant supply of spares, replacements, etc. What else can you do when Nokia might end-of-life a set of hardware you rely on in order to force you to upgrade to their newest stack? What incentive is there to put brand spanking new gear in rural Montana, when the three towers you have fill the market needs quite nicely?
You are assuming the company had good controls and processes around purchasing, etc. of fixed assets. They had developed some, but it is impossible to retrofit a comprehensive system of controls to an asset base that covers most of the continental US and spans multiple vendors and (former) corporate entities.