in the "good old days" (a few years ago) Verizon would give you a $200-$300 credit to upgrade every 24 months or so, as a sweetener when your contract was up for renewal. When you combined the contract renewal credit with ridiculous Black Friday sales, you could get a newer model phone (something that had been released in the past 1-2 years) for almost nothing - I bought a Samsung Galaxy S5 from Amazon for $1 total on Black Friday 5 years ago.
Now that phones are pricier and Verizon and other carriers got rid of contracts (and thus contract renewal discounts), shifting instead to monthly payment plans and phone leases, there's no significant incentive to upgrade every 24 months - now it makes more financial sense to use your phone as long as it can hold out until you can find a great sale or promotion for an upgrade.
I've been on a Galaxy S7 for almost 3 years now, and it still works fine for almost everything I use it for (except Google Maps, which has become ridiculously bloated). I'll probably hold out for a couple more months before shopping around for an upgrade.