Rox64 said:

But that doesn't explain why would the imperial fleet move towards the Death Star too, specially bigger ships like the Executor.

Why wouldn't they?

The only think that matters for the Rebels is blowing up the Death Star, not the battle itself. The best way to achieve the destruction of the DS is to move all your forces as close as possible to where the Fighters are trying to accomplish that mission and taking the flak off them (Literally). The Imperials would have to move off after them to continue the battle and protect the Death Star.

So again, why wouldn't they?