You can recycle, trade-in, or hand me down phones. It all goes to somebody eventually. The demand is there. Someone who can’t afford the latest iPhone will always buy my iPhone Upgrade Program refurb every year.
Now cases? Those are hardly reused due to the griminess and wear (no demand), and many aren’t recyclable. Though I have handed down some cases with devices to relatives if they were still in good shape. But they are often replaced due to personal preferences for style.
If Apple actually cared, they would provide at least security updates for old phones for a few years so older devices could keep going. Or, you know, make an iPhone that’s not two breakable slabs of glass on both sides. Or, at the worst, make an iPhone Ultimate that doesn’t need a case because it’s so rugged!