One fiddly bit per piece, as opposed to three, or seven.

The diagonal half-tiles can be paired up to form extra floor tiles. The round half-tiles can be paired up to form a nice circular pit. So they are a bit more useful than they might seem at first blush.

The thing about designing modular pieces is that you need to play around with them, and put them in unlikely configurations to see how they perform (or don't) in various combinations and positions, and not just the ones that make sense right away.

Who puts a 2"x2" room inside a larger room? Someone who wants to create a(n awesome!) vault -- and now you consider making a tile with three walls in a "U" shape. (Which, BTW, would make a nice end cap for narrow passages.)

Who puts up a row of corner pieces on one side of a room? Someone who wants to create a cell block -- and suddenly you need narrow doors.

My hope is that DF will keep things as simple as possible, using as few pieces as possible, to create as few sets per line as possible. We like to joke about "the addiction", and talk big about buying whatever DF puts out in resin, but the fact is that the number of sets in each line is actually one of the barriers to attract new customers. It isn't just the cost per set that keeps some potential customers from buying, it's also the number of different sets they'd have to buy to complete a particular environment. If DF wants to appeal to a wider audience and bring Game Tiles to all gamers, they need to keep a wary eye on the number of pieces and the number of sets they produce in the Dwarvenite product lines.