Curious as to the reason myself.

IGNORE
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Only thing that comes to mind is modem location has one Ethernet to area where switch needs to be located and the modem location is a WiFi dead zone or would require even more additional Eeros to get full WiFi coverage then if you could hardwire the Eero after the switch more central.
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I had to edit what I wrote cause the more I think about it I don't get why this is needed. Especially because there would be 2ea networking cables then between the switch and Eero(router) location to do what was asked. There also is at least 1 networking cable running between the modem and switch then as well.