It Depends how you measure "extremely serious photographers". Starting from Nikon d610 you have descent quality on sd-card plus portability in the same time. I understand that you can't put all the ports in the world in the laptop and while CF Cards reader would also be useful for photography I think sd-card reader or even micro-sd-card reader gives a compromise for mobile solution that covers many needs. Lack of this sd-card reader gives additional headache and nothing more useful as I see it.

Exactly. And since we might carry more than one model of camera with dissimilar memory cards, the Mac could need 3 or 4 slots. That’s why the good pro photo USB-C adapters have 3 or 4 slots.

Further, those readers seem to be made /just/ fast enough to read ahead of the current speeds, so when new speeds come out, you need a faster reader. That works fine if you have a USB 3.1 or USB 3.2 adapter, but not so great if the reader is built into a laptop with an otherwise much longer life.