Do you mean their cinema camera that has swappable mounts including DL mount, L mount, and M mount all coming first-party from DJI themselves? And E mount coming third-party rebranded by DJI? And EF and PL mount from third parties? If you go on any Ronin 4D user group, you will quickly see that Sony E mount seems to be the most popular followed by L mount.
I think you're just flat-out wrong on this, sorry. DJi have a total of 6 lenses for DL mount, IIRC. 16/2.8 (APS-C), 24/2.8, 35/2.8, 50/2.8, 75/1.8, and 17-28/4 PZ. These lenses are generally considered mediocre - I have had every one, sold the 16 (since cropping for it is pretty redundant with 24 on FF) and returned the 75 after verifying that it didn't fix the autofocus lag I was getting on a manual mount Leica lens. The whole point of those DJI lenses (except the zoom) is that they are very light weight and designed to be aerodynamic - I use them when mounting the R4D on a car. I like the 17-28, but it's really a focal length that basically screams "use me on a gimbal" and would have everybody instantly demanding a 24-70 ASAP.
There two third parties who have made a small number of lenses for the mount, the most interesting being Viltrox who have a set of f/1.8 lenses. This would put them in the position of having to play huge catch-up on lenses since everybody else has a many years-long head start and it'll be a major uphill fight to get third parties like Sigma to make lenses for it, given the lack of market penetration.
So it makes perfect sense that DJI would release a new camera using a mount that they already support and offer on their cinema camera. That or that their cinema camera would just support the mount system for the R4D and all of the mounts that go with it.