They specifically don't want to have too many SKUs to manage. Adding an option for an extended battery would double their SKUs. The management side of Pine64 is pretty barebones.
Both of those positions are valid. Bigger batt for $50 more would be great, vs meeting a price point and fewest possible skus.
I would yoink one with the biggest battery possible too.
But I would aslo do the same for several other upgrades that I particularly value. I would take as much ram as they want to offer. I would take as much ssd space as they want to offer. I would take as much ssd speed, cpu, pixels, as they can deliver. I would pay whatever it takes to make it weigh less and be smaller while still doing all that. And don't forget to put at least 2 full speed usbc/thunderbolt/hdmi ports so I can have external portable monitor without drivers.... Then again I don't want touch, or any form of face or fingerprint, or any more than the minimum gpu to run a traditional non-compositor desktop and display video at 30fps.
But now I have completely obliterated the entire concept of meeting a target intersection of functionality and price. I've thrown price right out the window.
And, that's just my personal individual set of priorities. You don't care about half the stuff I would pay anything for, and you probably do care at least a little about stuff I actively don't want. (gaming gpu, touch, face id, hell webcam at all)
So, back to the beginning, they came up with a reasonable set of functionality to target, and a reasonable price to target, and really, even though I too would like a big battery, it makes no sense to talk about $250 version that has a bigger battery.