Why attach streaming devices to Orbi satellite ethernet ports?

I agree with ekhali that wired connections are usually preferable to wireless connections, and that how you connect these devices to the satellite will have no effect on throughput, whether your backhaul is 5G or wired ethernet.  Both backhaul methods totally dwarf your 100MB ISP connection. 

My (personal) opinion is that Netgear put ethernet ports on the satellite (1) because the hardware already supported them and they had space for the ports, so "why not", (2) in fact, it could be exactly the same circuit board as in the router for all I know, and (3) there are LOTS of devices that lack WiFi.  With WiFi chips being so cheap and small, "modern" devices of all types have gravitated to WiFi for all the obvious reasons.  There are plenty of old PC's, Mac's, printers, etc. that were built without WiFi and this makes it possible to connect them (not convenient, maybe, but possible).