Despite the best of plans, ERP implementations often go wrong because customers have unique requirements that are always evolving and vendors will haul out the sledgehammers to force their solutions to fit - even if they weren't designed to deliver what the client wanted in the first place.
It's like trying to squeeze a watermelon into a small cup. Keep forcing it in and you'll end up with nothing but a messy pulp.
Every company is different. They compete in different markets, have a different target audience, and need solutions that support the different verticals they play in. No one solution can ever fit all.