There isn't "plenty" of availability for Infinity MileageLands. The EVA website does not reflect actual availability (that's why it says "unconfirmed"). You need to call EVA to check actual availability.

Business class award availability is just very limited right now, given reduced capacity and pent-up demand. EVA releases more of its partner awards very close to the departure date. For example, if you check right now, you can probably find an award seat departing TPE to any of IAH, YVR, SFO, or LHR, all leaving tomorrow.