Most ERPs can be quite flexible too, there's a ton of customisation possible. And a whole cottage industry of addons and integrations for every imaginable integration or business model. But the problem is you really screw yourself with added complexity when it's time to update. Then you're really condemning yourself to spending millions on consultants at a time when you might not have the resources. And postponement leads to technical debt.
Hence the idea of adapting the business to the system. Making sense too if you think about it this way: you're not really just buying a system but a methodology.
And another thing is that it makes integration with other companies easier. Makes the company more easy to sell or too acquire other companies and integrate them.
