Why does Abhidhamma exclude becoming, birth & death from 'mutuality'?

The Abhidhamma says: > 2.4. The Mutuality Tetrad > >PTS cs 246 > >With ignorance as condition there is a (volitional) process, also with a (volitional) process as condition there is ignorance, with a (volitional) process as condition: consciousness, also with consciousness as condition: a (volitional) process, with consciousness as condition: mind and bodily form, also with mind and bodily form as condition: consciousness, with mind and bodily form as condition: the sixth sense sphere, also with the sixth sense sphere as condition: mind and bodily form, with the sixth sense sphere as condition: contact, also with contact as condition: the sixth sense sphere, with contact as condition: feeling, also with feeling as condition: contact, with feeling as condition: craving, also with craving as condition: feeling, with craving as condition: attachment, with attachment as condition: craving, **with attachment as condition: continuation, with continuation as condition: birth, with birth as condition: ageing, death, and so there is an origination of this whole mass of suffering**. > > https://suttacentral.net/vb6/en/anandajoti#pts-cs246 Why does Abhidhamma exclude continuation (becoming), birth & death from its 'mutuality' above?