You can do that, except now you've moved the bulk of the work from the GPU to the CPU -- triangulation is tricky to parallelize. And GPUs are best at rendering

You can do that, except now you've moved the bulk of the work from the GPU to the CPU -- triangulation is tricky to parallelize. And GPUs are best at rendering large triangles -- small triangles are much trickier since you risk overdraw issues. Also, typical GPU triangle antialiasing like MSAAx16 only gives you 16 sample levels, which is far from the quality we want out of fonts and 2D shapes. We don't have textures inside the triangles in 2D like we do in 3D, so the quality of the silhouette matters far more. That said, this is what Direct2D does for everything except text.