Apple supports their devices for 5 years. Android it's more like 2 or 3 and often much less. And with Apple's retail presence it's easy to get 1-1 support which is non-existent for anyone other than Samsung. And with the extraordinary performance of their A CPUs often their devices are holding up longer as well.
Or even in most cities there are phone repair places that will get you a new battery pretty cheaply.
One big problem is that you don’t know whether you’re getting genuine parts, and aftermarket stuff can be quite crappy.
(Obviously the new phone would have other benefits, but it’s a big price jump. Even for a refurb.)
The average person has their phone less than 2 years. If we assume a normal distribution and a standard deviation of 11 months then 83% of people will keep it less than 3 years. 5 years would be 3 std deviations. That is a very small number.