There is a reason that appliances, or pretty much any product these days, do not last.
What is happening here is different - it's a question of "how do we make it as cheap as possible and last as long as the warranty".
They sound the same but they really aren't. No one is designing these devices to break deliberately. But companies absolutely are swapping metal cogs for plastic ones because a plastic cog won't break during the warranty period and that's what matters.
Real planned obscolescence is making software that requires online authentication and then switching off the auth servers 3 years in so that the customers have to buy a new version. That's a deliberate action.
It can be both. I was in a hardware store looking at painter ladders and noticed many of them had the two sturdy metal ladders kept together by a piece of plastic. Pretty much everyone would think they were extremely durable, while actually the weak link would soon wear to make the entire product useless. Was it incompetence or planned obsolescence? I have no idea, still I wonder why I spotted the problem in 5 seconds straight although I am no engineer.
Those do not like heat, and if you model the heat correctly, you fit the bell curve of expiration exactly after the 2-3 years after the warranty expires.
If you improve the cooling of the area, most devices lifetime can be doubled. I always wondered why no repair shop takes advantage of this, by offering a doubled warranty, for defusing planned obsolescence ahead of time.
An easier thing to do is remove the heat better. This can be done by making sure that the intake air first cools the capacitors (outside air->caps->transistors). Since most power supplies these days are shoved into a plastic box with no venting, it can be easy to add a few vent holes and a small fan. If you do this, make sure that all of the capacitors are discharged before handling as not all power supplies have bleeder resistors to make sure the capacitors self-discharge in a reasonable time period.
So yes, strictly speaking they are not the same and they can lead to different outcomes, but I am not sure how much of a difference it makes in terms of real world results. Sure, it depends on the cost structure of the product and a few other factors, but in the end many products will just break right after the warranty period.
That gear isn't plastic because it's cheaper than a metal gear, it is a sacrificial part.
Suppose you get some coffee beans with a rock in them. The burrs seize up because they can't grind the rock, and you don't notice it in time to cut the power.
Imagine that every part in the power chain is as sturdy as the motor and the burrs. The motor may burn out, or else it manages to force the burrs to turn, ruining them.
Now you have to replace either the expensive motor or the expensive burrs.
Instead, the plastic gear fails, saving the motor and burrs. This gear is cheap and easy to replace. (Baratza may send you one for free, even if the machine is out of warranty. Their customer service is second to none.)
So there are some cases where a breakable plastic part can avoid damaging or ruining the more expensive parts.
Of course one could imagine other ways of solving the "grinding a rock" problem. Maybe some kind of sensor to turn off the motor if it seizes up? But that would increase the cost of the grinder, and who knows if it may have other failure modes. Since this is such a rare situation, the sacrificial plastic gear is a simple and effective solution.
People make replacement out of brass. I shudder.
A better solution than a replaceable gear.
1. They don't want consumers, or third party repairs, seeing Factory Repair Information. (They pick, and choose which appliance repair shops get the information, and it's tied to sales. Try finding a independant repair shop these days?)
2. They usually don't sell parts out side of warranty. When they do, they are marked up very high. (If enough models were sold, the part might have a genetic equivelant.)
3. It seems like they make repair just difficult enough, so people just buy new again? I have a family member who admits Bosh appliances are overpriced, and have short lives. She still buys the brand? I believe Bosh psychologists know why?
4. Right now I have two Bosh appliances on life support. I fool around with electronic repairs so I have them kinda working. If you get an E13 error on a Bush Washer, it's usually the drain pump. In order to open the door, you need to shopvac the water from the drain hose.
5. I've noticed the weak spot on Bosh appliances is the computer, and I get it. It's not the best enviornment for electronics. Make the computer boards similar to vechicle boards. It's pretty rare for a vechicle's computer to fail. Meaning they are built for a nasty environment.
On the other hand I have a cordless Bosch drill/driver set I bought refurb, they've held up to years of neglect and (not pro) use. Maybe give them a try next time?
Edit: jokes aside, that's good information. Fwiw I had to babysit a little tube for an hour+ to drain a Samsung washer to get at the drain filter. I wish I could have used a shop vac to speed that up.
They are choosing to ask this question.
But it's possible to ask other questions.
Let's take the example of the Gigabyte "Ultra Durable" mothers.
It's a motherboard series with some improved parts with a focus on reliability. And they are relatively cheap parts. And supposedly the really increase the reliability of this motherboard.
And they've built an affordable brand around it.
And people like it.
Except if you design something to break right after the warranty (or as close to it as you can get using the cheapest materials possible), that is what you are doing.
So your only reference point is seeing that all the older appliances seem to be built to last. You'd need to do research on all the options that haven't lasted to today to find out if modern stuff really does break faster, and that's much harder to do.