You can replace parts that don't come in nice detachable sockets.

Lightbulbs came in sockets because they were meant to fail. First by accident, later intentionally. They were also quite breakable because they were made of glass. LED lights don't have these problems unless they're designed to. Which is the meta-problem - how do you know which ones are planned obsolete?

Forcing an LED system into a lightbulb from factor has quality and cost implications though. A good LED light has a separate power brick inside the enclosure. Which is what you see in these fan lights.