AFAIK, they introduced SAP elsewhere in the company, and it became difficult/too expensive to manage the communication between the old system and the SAP system. I can imagine too well how the conversation between the SAP people and the company went because I also took part in similar conversations with clients in a previous job a long time ago: client asks you if software X can do thing Y. Both you and the person representing the client have only superficial domain expertise on Y. "Oh, you mean enter data into a form? Of course software X can do that, it was designed exactly for that purpose!"

The complexity of the task is eventually discovered in production.

If it was like typical ERP/MRP rollouts...

The short answer is that a sales guy in a nice suit took some execs out for steaks and more than a couple cocktails.

The long answer is that management, these days, is trained to outsource everything while still being clueless about what the people they're replacing actually do.

In-house tooling requires a dedicated team, not just developers but also analysts, testers, etc. Often a company inside the company.

If the software needs to change due to industry changes or regulations or something like that, it will probably be a lot more expensive to implement it yourself compared to using an off-the-shelf tool developed by a company who's sole purpose it is to respond to those kind of changes.

Working in a large corp, I find IT consultants from the outside overpromise and underdeliver on projects

It’s infuriating as anybody below senior management can see right through it

Their most succesfull salespitch to the CEO is that you're not a real company untill you join the SAP club.