Yeah, unfortunately Asus took that away a couple of generations back. It's the main thing that keeps me away from their more recent phones.
I can sort-of understand omitting microSD support in a "compact" phone that's targeting a more mainstream market, but the part that really boggles my mind is that they've never had a microSD slot in any of their "gamer" ROG phones. Those things are huge, and also sold to a demographic that is more likely than average to want all the storage they can get.