They do. You're notified when battery health is either unknown or reaching EOL. It points you towards replacement, not upgrade.

"If battery health has degraded significantly, the below message will also appear: Your battery’s health is significantly degraded. An Apple Authorized Service Provider can replace the battery to restore full performance and capacity. More about service options…"

https://support.apple.com/en-us/101575

Apple provides a warning and a link to battery replacement options from the Battery Health screen when it detects that it's been degraded too much. So... they do provide this?

What a reductive position.

They could also include little leaflets about “Land Declarations” with iPhones and other such rubbish, but that does’t mean it would be a wise policy.