It could also be simply greed, where Apple just wants you to pay them and pay them only. Now it seems that Apple is about to make third-party repairs even harder, at least as far as replacing iPhone batteries are concerned. In a report from iFixit, it seems that in the event you were to change your iPhone battery at a third-party center, under the Battery Health section in your iPhone settings, instead of showing the percentage of your battery’s health, it will show “Service”.
This “Service” message usually appears when your battery has degraded to the point where it needs to be replaced, but in this instance, the message appears even when a new battery has been put in. This is regardless of the fact that the battery in question could be a genuine Apple part.
What this means is that if you had sent your iPhone to an official repair center, the technician would then have the ability to “authorize” the repair process and to clear the “Service” message. According to iFixit, “This “Service” indicator is the equivalent of a “Check Oil” light that only a Ford dealership can reset, even if you change the oil yourself.”