It's a great point. Nikon has always maintained that the capabilities of the Z mount are as important as mirrorless camera technology itself. The mount, they claim, offers them the opportunity to design optics that were never possible before. They may have a point - other than the halo product of the 58mm f.95 (who will buy it, anyway?) Nikon seems to have produced some of the sharpest lenses anyone has ever seen, from any vendor. I don't know what advantages larger throat diameter and shorter flange distance offer for long glass.
Interesting times
There are very important reasons for the larger diameter lenses and lens mount across the board, there are experts that can add more scientific facts, however from a simple hypotheses of mine, the principals relate to..........
Light is a photon made up or red green and blue, the more light the better everything is.
1) faster easier more transmission of light edge to edge equals better edged to edge sharpness and tracking performance especially needed for video.
2) easier/more transmission of light equals better focus speed and accuracy.
3) it just adds more light performance which equals better more accurate colours and less ISO needs not friendly to Video, I mean Nikon knows Video is the future especially for sports action ..........period.
4) it allows for better balance given the Z bodies are smaller and lighter.
5) here is my Leon Musk mentality moment showing.......its future proofing, a drop on the opposition who have tooled up and made lens that suites the old 35mm narrow mount, Nikon tooled up and made for the new generation of Z lenses with no determent lenses and bodies that can jump to other than 35mm sensor sizes, ie: they can go to a 40 mp DX equivalent medium format sensor, this should have the drop on the Sony and Canon mob should they wish to catch up........also Sony and Canon will need to resell new lenses a second time to catch up to Nikon, this wont go down well wit Sony Canon owners.
As for the Z9
The end game...if the Z9 comes out with 40 to 60mp with 20-60 FPS with accurate focus and tracking it will make all of the Nikon gear currently used totally obsolete for sports action wildlife, Nikon would then introduce refreshed versions of the Z6 and Z7 containing the key features of the Z9 at a affordable price......Bingo there is the 3rd sting.
The industry Pie is not big enough for the G3, the near future main game is with a minimum bet table now calling for 50-80 mp 30-60 fps and first-class video with full G5 G6.... 8 k with video direct connectivity or you will need to get out of the game.
I feel it will be 2022 to 2023 before we see a string of affordable enthusiast drill down models from the Z9 new technology assuming its even successful or better still exists, I pray it dose.
A digressing thought, Driving to Hanover airport from Delmenhorst Germany to catch a flight, the V8 Audi was beautifully and controllably sliding nicely sideways on the entry ramp leading on to the expressway, nice traction control, it was raining and super dark no overhead lights late in the evening, two weeks after landing home in New York I got an A4 sized letter in the mail with a huge speeding fine, thinking I could getaway with it by saying my German girlfriend was driving, sadly no, as on page two there was a lovely super clear portrait shot of my face clear, eyes open, both hands on the steering wheel, the face image was in a 3 inch circle the rest of the page outside was black .....120klm on a sweeping bend taken from a two inch size square sensor that looks similar to a normal reflector hidden on the armco.....safety rail, there was no flashing light that I ever saw, so how the hell can that be possible. My friends in Germany said yes you cant see them they are highly accurate. That was 20 years ago, so the technology is there, why aren't we seeing it............
Only a Hypothesis and opinion
Oz down Under