Because (1) compute requires newer hardware than what would be ideal; (2) compute cannot take advantage of early Z, which is critical for SVG (neither can Slug

Because (1) compute requires newer hardware than what would be ideal; (2) compute cannot take advantage of early Z, which is critical for SVG (neither can Slug or GLyphy, by the way); (3) the two step process is hostile to batching. Slug is asymptotically slower than Pathfinder at fragment shading; every new path on a scanline increases the work that has to be done for every pixel. (Of course, that's not to say Slug is always slower in practice; constant factors matter a lot!) GLyphy is an SDF approach based on arc segment approximation that does not do Bézier intersection at all.