Sorry for wastIng you guy's time. It was a fuse in the engine box. Not sure why or when it blew, but completely overlooked that one. Still going strong after 100+ miles.
Side note, Smart Subaru quoted me a new fan for $359 after a test drive and noticing the fan was not spinning, but Autozone helped me diagnose actually recommending connecting to battery to test before spending $110 on new fan. Their tech helped me remove the fan and test on the battery. Good customer service.
Makes sense to be fused separately when one thinks about it. Why put them together such that a 30 cent fuse could be a common cause failure that takes out both fans. The more independence each can have, the more redundancy. As the OPs situ showed, one fan is enough to prevent overheating.
They both always run at the same time, either in low or high speed.
When the ECM calls for the fans to be on low speed, relays are used to connect the two fan motors in series. That reduces the (common) current through the two motors, causing them to run more slowly. The current for both comes through one fuse.
However, when the ECM calls for high speed, the relays are changed. The original fuse used to power both in low speed will power only the sub-fan (right/passenger side). The power for the left side fan comes from another fuse. As both fans are now powered separately, they get full current and run at high speed.
Consequently, if the fuse used for slow speed is blown, then when the ECM calls for slow speed, neither fan will run, but when calling for high speed, the sub-fan won't work, but the main fan will.