For example, under the Consumer Rights Act 2015 in the UK the product must last for as long as a reasonable person would expect it to, and Apple's interpretation of that is five/six years (see https://www.apple.com/uk/legal/statutory-warranty/).
The Consumer Rights Act 2015 also covers unfair terms in sales contracts (and at least in Scotland EULAs are part of the sales contract, per Beta Computers (Europe) Ltd v Adobe Systems (Europe) Ltd; I don't know the status elsewhere in the UK), and it's quite likely you could just go through most of the possible contractual outs and argue they are unfair terms.
And they are more expensive than many computers you can buy on the market. 2 years support on a device that can cost $500+ isn't acceptable.
We are 4-5 years into the period where people have had sub $300 choices, so there is an alternative to spending $500+ on a device that comes with 2 years of support. Maybe not a fantastic alternative, but the $300-$500 extra that people choose to spend says something about what they care about.
You don't know that. Apple could very well release an iOS 10 update for this.
But in both cases the stated policy is that the devices will not receive any more updates, either feature or security.
There is a problem with handset abandonment, but this is true across all vendors, and it does not underline sequence7's claim that this is solely an Android problem.