Mmm,
Nikon 'We've made an adapter that allows you full compatibility with 90 of our own lenses, and a couple hundred more have partial compatibility'.
Random person 'That's great, but can't you give all the technology for that adapter you have to other companies to make it easy for them to make adapters?
Nikon 'How do we make money from that?'
Random person 'You may gain users of other camera systems.'
Nikon 'Are these people buying our lenses when they buy the camera or just using somebody else's lenses with an adapter bought from someone else?
Random person 'I don't know'
Nikon 'Neither do we, so we won't make it easy for people to spend lens money elsewhere. We'll look after our current users first to make the transition to Z mount as easy as possible. We've made the largest lens mount that could be adapted for almost any lens, but we would prefer it if you used our F mount lenses before anything.'
Random person 'But I want to use ****** lens!'
Nikon 'And if someone works out how to do a quality adapter you will be able to.'
Random person 'But Sony have an adapter and also helped people make adapters for other lenses!'
Nikon 'And how many new lenses did Sony have on release of the E mount, and how many lenses did they have in their Sony/Minolta lens history?'
Random person 'Erm, five new lenses I think, not sure about old lenses.'
Nikon 'So I think what you are saying is that they had five new lenses and a few older lenses, but thought it was beneficial to be able to use other manufacturers lenses to be used on their system until they brought out their own versions to flesh out their range, so shared with other companies how to do it easily?
Random person 'Yes, that's it exactly.'
Nikon 'We don't have to do that, did you not understand my previous answer, we have 90 lenses fully compatible, and a few hundred older lenses which should cover what most people need for now'