Most LEDs run on DC, and the built-in transformer is the most likely component to fail. If the LED is failing and getting dimmer, it’s most likely due to poor heat dissipation.

If we had little 12v adapters and separate LED modules, you could reduce waste by only replacing the part that fails, and manufacturers would have greater incentive to improve build quality. Instead, we get cheaply manufactured bulb-shaped disposable units that need to be thrown away when one part fails.

LEDs themselves don’t get dimmer and don’t fail. Their drivers fail and run LEDs at higher voltages so then LEDs burn out. If the LED is driven correctly, it won’t dim over time and will last pretty much forever in terms of human lifescales.

I’ve had lots of led bulbs die. I think it’s because I bought them at the dollar store.

Usually it’s a badly designed heat sink that’s meant to cause an eventual short so that it has to be replaced. Or just shoddy low material builds. LEDs really can last an obscene amount of time and they don’t die another part does.