There have been a few cases of planned obsolescence over the years. However, I think the key issue is that people don't generally re-purchase products from suppliers who produce unreliable goods. Quality is seen as one of the more important factors that consumers consider when purchasing a product, and while price is also a critical factor, that creates a balancing act for manufacturers.
For instance, while I am sure car manufacturers have considered making unreliable cars to sell more cars, they ultimately spend an enormous amount of money making their vehicles last for a long period of time, because it is bad customer image if their product only lasts 7 years.
Manufacturers have a perfect "out", especially with household items-------- they simply reduce the quality of the "prestige" brands, so that they are just as bad as the "El Cheapo" option.
The mugs, sorry, "valued customers", sick of the short life of the latter, then pay a premium for a "Sunbeam", "Philips", etc, which doesn't last any longer, costs the importer the same amount, but retails for three times as much!
Now that all the "grand old names" have been whored off, that isn't hard.
Customers eventually accept that they might as well buy the "El Cheapo".
They are still paying more, overall, as they have to replace each device much more frequently, but are no longer getting suckered in by the "premium" brands.
Interestingly, there are still a few well engineered "El Cheapos" around, which have quite respectable lifetimes.
Finding them is the hard part!
I got suckered when I bought a "Wertheim" vacuum cleaner, a so-called "top of the line" model which was purported to be "German designed".(After all, it had a nice "pretend" German name,)
All I can say is the designers had never seen the inside of an Engineering classroom.
More likely drawn on the back of a placemat at the local boozer!
Needless to say, it was bloody useless, never operating for more than10 minutes before overheating, the hose continually blocking because the dumbos ran the wiring for the "power head" loose though it.
(Our little 15 year old Toshiba had wires running in the hose, too, but they were embedded in the wall.)
The Wertheim was chucked into the shed, & the poor, old, long suffering Toshiba put back into service.
After a few attempts to fix the POS, it went to the verge rubbish pickup.
After some years, the venerable Toshiba finally failed, & was replaced by a $A50 "Ozito"canister vacuum cleaner, which has worked admirably for several years.