Great question — answering as the UphillTech team:
Is it ever explained who operates those stations, and for what reason? It is! This is a massive spoiler for the Season 3 finale The Day We Died so reveal at your own risk: It's Walter (plus Astrid & Ella) from 2026 who are ultimately responsible - they use the wormholes to send the parts of the Wave Synch Device back in time along with seeding the coded location info of the parts to then be propagated by people like Sam Weiss' ancestor and ultimately broadcast via number station so that the Fringe team will pick them up, and ultimately assemble the machine for Peter to use. This results in the creation of the "First People" myth, the mistaken belief that the machine is a Doomsday device and...
Full answer by motosubatsu: https://movies.stackexchange.com/a/132373 (CC BY-SA 4.0).
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