/data get entity @e[type=minecraft:minecart,limit=1]

The cart with a "player" passenger doesn't display this in its nbt data. See the attached screenshot. I am clearly a passenger of the only other entity in this test world, the minecart.

When it has a mob passenger, it properly displays that in its nbt data.

I have been troubleshooting a mcfunction that needs to detect a minecart carrying a player when I discovered the minecart doesn't "know" when it has a player passenger.