The major engines may not have ECS built in, but some of them are supported by ECS systems that are readily available. Your implicit restriction of professional gamedevs to include only people who both use a major game engine but don't use third party components not supplied by the engine is, I think, overly restrictive.
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.
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.
That Unity and Unreal are lacking (even after Unity's public efforts in the area) is because they are licensed en masse and retrofitting each with an ECS would be no small feat. And is that refactor worth losing revenue from obsoleted marketplace content? Or does the ECS need to interoperate perfectly with existing code from endless numbers of existing projects while still providing the benefits of a dedicated solution?
Unity and Unreal are not the only engines. In house engines are shaped by the needs of the immediate users, and not the sales pitch for hobbyists or third party studios.
[0]: https://www.gamedevs.org/uploads/data-driven-game-object-sys...
Unity has not shipped DOTS. They actually removed it from the Package Manager last year. Joachim says it has a bright future, but I suspect it will never ship in Unity itself.
Epic has nothing in Unreal yet, though apparently a few months ago somebody spotted some changes in repository that suggests one may be on the way.