With no new device, they had no revenue coming. Perhaps a subscription model would / could have worked: pay something, say 20 EUR per year or so to get updates even with the old device, and be able to carry your subscription to your next phone if you want to run SailfishOS on it. I'd happily buy a Sony Experia Experia Z5 AND pay Jolla a separate fee to not have to run Android on it.