My understanding is that Apple has not tried hard to sell the Mini. Or, said differently, their strategy of trying to push people to the most expensive models is working too well. Removing the mini will disappoint those who do not want that large and expensive a phone, but still a modern design. Unless the SE (version whatever they make at that time) takes the space left empty.
Many people do. I am using a 6s I bought about 4.5 years ago, am still happy with it, and am planning to using it for at least one more year, if not longer. Released in September 2015...