Some people say when you close yours eyes it's like a wall that would be very close: if you throw a ball against the wall it returns immediately and it is difficult to control. It would happen the same with thoughts. Hey, this is an explanation ... I have not found very persuasive by experimenting...
Now, if you keep your eyes open and fix a point about 30cm in front of you in space, you will see that:
1. it is not easy
2. it helps to focus significantly
Finally, other explanations are related to channels and energy which would be connected to the eyes. By keeping your eyes open, we allow this energy to mix with the space. You connect the inner space to outer space. it greatly facilitates the overcoming of the feeling of ego.
That said, those who lean in favor of closed eyes have certainly arguments even more convincing.
The most interesting is perhaps the question at a time: why I like to meditate eyes open (or closed) ... And change