Here are things upper management doesn't consider:
* Picking the same ERP solution everyone else in your industry uses means you have zero competitive advantage now. Homegrown solutions with teams staffed to run them could give you an advantage.
* You need to pay expensive consultants to do things with ERP. If you want any customizations they will be a bottleneck for all future updates, possibly having to bring in expensive consultants every time you need to upgrade.
* The culture shift for employees is usually negative across the board. The IT people supporting it, the end users inside the company, basically the choice implies that management doesn't value its people or their thoughts on how to do their work.
* Vendor lock in. Switching from one ERP to another isn't likely to happen. They can raise their licensing/cloud costs when contracts are up and your company is likely stuck.
It would be like interacting with other people who knew based on the average of everyone on Earth as opposed to dealing with the person you knew based on their own personality.
But it's easy to manage based on these kinds of broad generalities and, as the saying at least once went, no one gets fired for choosing IBM.
"Successfully lead SAP implementation bla bla bla saving bla bla bla streamlining bla bla bla"