The benefit is to the developer, arguably the most important part of the game development process. It can save a lot of headaches that OO hierarchies can create, makes things more easily concurrent, allows for more flexibility in behaviour and emergent gameplay.
ECS helps to prevent bugs in game object logic, by keeping state and behaviour separate from its corresponding entity. If I'm looking for some behavior, I don't have to start thinking about which ring of the inheritance chain it ended up on, I just find the component or system that does that thing. It encourages you to write state and behaviour in a way that works with any entity and can be attached to anything at any time without crashes and state mutation problems or race conditions.
A traditional OO architecture will provide all the performance you need to create a modern Simcity style game without having to take on the additional problems of potential bugs in the underlying code, training everybody to understand and use it, and not even really knowing if the end result will be significantly faster or not.
Where I work we think long and hard about adding any third-party packages to the project. The benefits have to be very real, for the budget or for the player.