Possibly not, but the hazards of software procurement bite bigger at that kind of scale, and it's an under-studied science with not enough assurance of quality outcomes. I'm sure that 'x percent of IT projects fail' metric has improved at least somewhat in the last couple of decades but it's still fraught with pitfalls. Not uncommon to end up with an end result only as good as, or even potentially worse, than the one you were rushing away from. Better the devil you know, and all that.

Regarding altenatives at that scale, I've not been involved in a project at that kind of scale, biggest SAP implementation I was involved in was ~10k employees and Alphabet is sitting at ~130k right now. I don't want to dive too much into speculation, perhaps Google will get a good outcome with this approach and since they're coming from a bad place with Oracle the future might still be crap but perhaps just a bit less so.

The biggest issue with procurement of SAP and it's ilk is it shifts a fundamental burden from procurement to implementation. With a defined software/SaaS solution that's ready to go out of the box, you get to answer a lot of the yes/no functional questions at procurement stage. It can do it or it can't do it and you get to decide how important that is to you. With SAP, every requirement is answered with 'it can do that' with the massive asterix that to make it do what you need it's all going to need to be customized to do so. That opens you up to a lot of risk IMO.

Thanks for the detailed answer. I hadn't thought about the shift from procurement to later in the life of the product.

Sure. Make it yourself. Very easy. In several of my companies we would create our own business layer, without the SAP bullshit.

It's cheaper, it's faster, it doesn't need training and cheat cards, it's self explanatory, and you can maintain it by yourself. Plus you know it inside out. Plus you can add much better features, like graphical reports on top of it easier.