Aspect Ratio for Social Media (DJI Action 6)

Yes, I am sure you guys might get this question often but I apologize. I am more so asking to see what I did wrong.

Looking online, alot of people recommend recording in 4:3 or 1:1 open gate when your end goal is social media (tiktok, instagram reels) and then later crop to 9:16 whenever you are finished.

I tried something similar and recorded in 16:9 originally (car content) and later cropped it into 9:16 and the resolution downgraded from 3840x2160 into 1214x2160. I then realized I could just record right away from the camera into 9:16 and did so, and the video came out 2160x3840.

If that is the case, why is it that people record in 4:3 or 1:1 when they could do it in 9:16 natively. If I am missing something, please let me know. I am learning and just recently got the DJI Osmo Action 6.