Simply because the eMMC is faster and more durable.
- Flash Jumprive to the MicroSD-card using Etcher.
- Put back the MicroSD in the Pinephone and boot with it connected via USB to your computer.
- Flash the distro image using Etcher, this time you pick Jumprive as target.
- Remove the MicroSD-card from the Pinephone, otherwise it will boot back into Jumprive.
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