I hope this helps someone else. I thought I just had bad bulbs!

LEDs with electronic controllers (basically any bulb with base) are exquisitely sensitive to heat. They have really good heat sinks. But they can overheat quickly in enclosed fixtures.

I have lots of old fixtures in my old house. I don't want to change them. There ARE bulbs rated for enclosure. Most are really expensive, but it turns out some cheap ones from Home Depot made by TCP are enclosure rated.

I'll update if they die!