It's not "Apple's" service, for starters; the website very clearly states "The online store is operated by a third-party provider authorized by Apple to sell genuine Apple parts and tools." (https://support.apple.com/self-service-repair)

Normally this is the part where you'd take your phone to a cost-competitive repair shop for the same fix-me-up. Except you can't, because Apple stopped selling those people phone parts so they could profit off this instead.

Caveat emptor, repair shops warned you for years.