There was a tendency at that time to isolate the final dungeon, possibly to reduce any temptation to get your party killed by tackling an impossible dungeon too early. It happens in MM5, and it happens also in MM6. In MM5, there's no reason to go near A1 early on other than sheer exploration - it's a bit like the Sea of Fire in Clouds. Even the skyroad doesn't go there. And IIRC, an approach at ground level is also pretty unwelcoming. I remember exploring north from Castleview rather than following the road east, and leaving northern A2 a jolly sight quicker than I entered it.
In MM6, the only reason you have to visit Sweetwater before you actually have to tackle The Hive is the "Place the Statuettes" quest, and you don't have to go far in to find that.
So they may have had a reason. It's debatable. I don't know. Anyway, by the time I got to the point where I tackled Castle Alamar, I was pretty well sated with adventure, and the putative lack of interest created far less frustration than the slog round those endless expletive deleted mines early on.
