“It losslessly compresses RGB and RGBA images to a similar size of PNG, while offering a 20x-50x speedup in compression and 3x-4x speedup in decompression.”
One person who says he is not a compression expert wrote an image format in about 300 lines of C. It matches PNG on size and beats it badly on speed. PNG carries decades of committee features almost nobody uses. Simple won because nobody had bothered to try simple.