In my mind, these companies are all so massive they can afford a little fragmentation for the obviously small market, with no meaningful impact to their sales numbers or profits.
On the iPhone minis, there's very obviously a market for them, but the market is so small compared to the market for "all iPhones" that it practically vanishes in comparison, which leads Apple to not bother. Is it really that expensive to maintain a more niche line for each generation?
Think of just the work that goes into having an assembly line customized for a specific form factor. To keep price, quality, and profit in line with their other phones I think the answer here is clearly yes.