If I'm on the go, I'll have to take it out of the chassis while it's in my bag so I don't damage it. In that case, it's easier to have a regular USB-C card in that port, and toss a dongle in my bag instead of the expansion card.
If I'm not on the go, I'm at a desk, and I'd still rather plug in a dongle than regularly swap an expansion card.
I'm not saying you'd never want the expansion card, but it feels pretty niche.
While a regular usb-c ethernet adapter has a flexible cable between the laptop and the bulky rigid part.
Anyway it is probably just there to demonstrate the possibilities to consumers. What if a lower profile standard for networking gets popularized?
No, you wouldn't. You'd have one of these instead: https://frame.work/products/usb-c-expansion-card?v=FRACCQ000... (or the one matching a color you prefer and your particular model)
Expecting it to work full time in a laptop is a bit of a stretch of the heat dissipation budget.
Also, the laptop he is working has the AMD FP8 chipset - depending on how the ports are setup, he might only get 10G USB, if the ports are allocated to video instead.