The LED bulb itself is not typically the reason that these fail. There’s also complex regulation circuitry which consists of far more complex components than a single LED. Electrolytic capacitors and driver circuits can have shorter lifetimes than the actual bulb.

With that said, manufacturers know this, so they also tend to overdrive lower cost LEDs to bring the failure rates in line with the rest of the circuit. This sounds like this may be what has happened to you just based on the dimming, but without knowing exactly how they have wired it up, it’s difficult to be sure.

There are multiple LEDs in the bulb and they're overdriven, meaning they're designed to fail. They can be modified to put out dimmer light that will last a very long time but that's not something most people know how to or will do. Failed ones like you describe are usually repairable also but same issue that most don't know how to or won't.

They fail like that because one element dies entirely which messes up the circuit. If the dead one is bypassed with a small resistor the others will light back up.

It's not the LED but the cheap crap components used in the controller.

Followup question: is there a company that is not part of the new lighting cartel making screws-in bulbs that actually last 10+ years?

It's by design so people buy more lights. It could be made to function better and last way way longer (theocratically forever by a human's standards).

But then the quarterly line won't go up high enough, so it's "bad for business".

Like someone else commented, even the bad ones can be made to at least be slightly better with small adjustments to the circuit, but then 2 people out of 8 billions around the world would be reluctant to buy the extra luxury package on their third super yacht. So obviously it's not worth it (╯°□°）╯︵ ┻━┻