I'll give just one example. A few weeks ago I took my baby to the doctor for a routine exam, which includes weighing.
Scales are an ancient, pretty straightforward technology. If a skilled craftsman built a scale 300 years ago and it was well maintained over the centuries, I think its reasonable to expect it to still work adequately, and a minimally trained person would be able to operate it.
However, this electronic scale was so complicated and full of gadgetry (including bluetooth) that the hospital staff were unable to weigh my child and we had to go back home and reschedule.
I can think of a million other examples (Juicero...) but I'm more curious to hear of real-life examples like the one I shared.
Best microwave I've ever used was made in, I think, the late 70s. Didn't even have a turntable, and worked just fine without it, somehow. No clock at all. The "UI" was two heavy-feeling knobs, one for power and one for time. Turn the time knob, and it starts cooking at your selected power until the time runs down, with the knob itself tick-tocking down to zero and setting off a physical(!) buzzer. Want to add more time? Turn the knob while it's still running, no problem. Realize you added too much time? Ditto, but in reverse. Exactly as you'd expect. Simply pull the door open, no button for that, even.
Intuitive, simple, felt great to use, and did 100% of what I want out of a microwave.
Basically anything that used to have real buttons and knobs that have been replaced by shitty-feeling rubber-covered buttons and knobs that merely communicate suggestions, hooked up to an embedded computer, has a worse UI than what it replaced. And don't get me started on touch-sensitive buttons. At least touch screens have some excuse, some purpose. Dedicated touch-sensitive buttons are like some kind of practical joke, and have been central to several of my worst experiences with products.