Attach the hub to your monitor's VESA mount points and you gain a lot of long-term flexibility at the cost of a single short wire that'll be hidden behind your monitor. Otherwise functionally identical to an integrated hub/monitor, but you can upgrade or replace the individual components on their own schedule.
A good monitor can last through generations of computer hardware, it doesn't make sense to combine directly with other components that have much shorter lifespans.
Isn't it the same number of wires, since you still need to run a usb cable from the computer to the monitor? So then really all you get is not needing a separate box for the hub. That's admittedly nice -- I have a Dell monitor with usb ports and I use it, mostly because I'm not going to buy a standalone hub when I don't need it -- but if the monitor had a way to mount the external hub on the back, I think that would be the best of both worlds.
One cable rather than two. Some monitors have integrated USB hubs, but you need to connect a separate USB-A to USB-B cable, in addition to HDMI/DVI/VGA. Newer, high-end monitors will transmit video and USB over a single USB-C cable, as well as power in the other direction (to charge a laptop).
