is there a reason why the P-cars don't/won't come with these sequential manual gearboxes?

i didn't know if they have one in development (most likely), if it's R&D costs (too much), or if they feel as though it's not worth the money (b/c high failure rate).

any input? just curious. 'prefer using my left foot myself, but am surprised, given the SMG2 in bmw's e46m3, that porsche hasn't pushed one out, too.