So what? They can still track you across devices. Especially if they use some 3rd party ad SDK, which might use the Google advertising ID, or some other identifiers.
Modern tracking is fundamentally a product of executing hostile code on your own device. The idea is to never put apps that have built in or will otherwise facilitate surveillance on the more secure devices. This includes a javascript browser, due to its unwieldy attack surface.
Separate devices draw a line in the sand, rather than just accepting amorphous insecurity as inevitable. And then you can work on slowly moving your usage patterns away from the surveillance-foregone devices.
If you use them to connect to your home wifi then they show up on the internet with the same IP. It's very easy to connect separate devices to a single user.
