It might seem, as some kids receive more than one offer (main round AND specialized), that when kids accept those specialized seats, that would open up spots in main round schools.
Every school, both specialized and main round, over offer. Schools know that not everyone they offer a seat to will accept. Principals have a sense of how many kids to make offers to/how many will end up in the school. I sat with Tech’s principal back in the day while he was figuring out numbers. He generally makes 500 or so more offers than they expect to say yes.