Explain Like I'm Five

That's not quite true: other parts fail more often. I've never once had a headphone jack or micro SD card slot on a phone break on me. I've had headphone jacks on other devices break, but pretty rarely. On other audio equipment, 1/4" jacks break all the time, but headphones jacks just aren't subject to that kind of force. I don't remember anyone I know personally having issues with those things. LED's are incredibly robust as long as you don't put too much current through them or invert the polarity. And you wouldn't want that much current for a mere indicator anyways.

The part most likely to break is the screen. Next is the battery, which doesn't break but rather wears. Next is the charging port (depends on the standard, but this is less of a concern recently with USB-C, Lighting, and wireless charging). Next is physical buttons (power, volume, etc). Then you start getting to the point of headphone jacks and micro SD cards. It's hard to find solid academic research, and a lot of this varies over time and by make and model, but a quick search turns up a bunch of articles from cell phone repair places that back this up.

Also worth mentioning that the CPU, RAM, and updates, along with the ever-increasing demands of apps a d websites, means phones that were powerhouses 10 years ago are barely able to do anything today even if the hardware is in pristine condition. That's a whole other problem, and others have pointed out the waste and evils of intent obsolescence. Related to headphone jacks, SD cards, and indicator LED's: that further invalidates the reliability and longevity arguments because those parts are going to last way longer than the main parts of the phone would anyways.