I think the main issue here is that they're competing with phones and the main differentiating factor is size, I can't think of anything I'm comfortable doing o

I think the main issue here is that they're competing with phones and the main differentiating factor is size, I can't think of anything I'm comfortable doing on my phone but not on my tablet. Most people would rather use one device than two. Android phones have long been available in larger sizes, iOS ones have since the latest update. Perhaps a natural result of larger phones is fewer tablet purchases.