The Spanish voice actors who dub "The Simpsons" are in a labor disbute with a Mexican contracting company. If a solution can’t be found, they stand to lose their jobs.
It would be strange if the existing Spanish voice actors were replaced by new ones after 15 years. You get used to the voices. It’s not exactly the same voice. An English Homer isn’t a Spanish Homer, but when you compare the two, it’s almost uncanny.