The problem, generally, is that rendering the tiles is computationally expensive. You have to wade through each feature (thing that could be represented in the

The problem, generally, is that rendering the tiles is computationally expensive. You have to wade through each feature (thing that could be represented in the tile) and decide if it intersects the tile, then decide if/how it will be rendered, then render and composite it with every other visible feature. Doing all of that work quickly is possible, it just isn't simple. Also, for most people the data involved changes relatively infrequently. Why have the server render the same tiles repeatedly when you could just cache the result and reduce it to a simple file hosting problem? Also, your 2048x1536 screen may likely be loading more than 48 tiles. It's common to request tiles around the current viewport and (less common) above/below the current zoom to ensure they're present before they're needed. To see this in action, see how fast/far you have to scroll a google map before you can "catch it" with tiles that aren't loaded.