At 8% of the iPhone sales share, the iPhone Mini probably sold many times more than any Google Pixel, and probably anything at all short of the Samsung Galaxy and maybe a Huawei model that never left China. That alone should justify its continued existence.
Not everything has to the best-most-seller. I've been hearing "Apple should discontinue iPad Mini" for what feels like a decade… people love them, people buy them. And if the iPhone Mini drops to a once-every-three-year cadence like the iPad Mini… that sounds great! That's exactly the right update cycle for most people and their phones.