Any simple gas mower you buy off the line today can last practically forever if you just do basic maintenance and store it properly between seasons. They are just pretty simple engine designs that haven't really changed in decades.
I used to be a groundskeeper, and as long as we kept the blades sharp and did basic engine maintenance like changing the oil and filter, we could just abuse a push mower all over the golf course for 50 hours a week summer after summer.
They design the mowers to vibrate apart after 10 years. The engine properly maintained can last a lifetime, but the rest of the mower will not. Golf courses buy a higher end mower (which isn't that much more money) which will last a lot longer.
No that's just poor product quality. Planned obsolescence is mostly a "meme" that confuses cost cutting by all possible means which results in very poor quality. Modern products are cheaper because they use plastics instead of metal but it also means that they are of lower quality.
I used to be a groundskeeper, and as long as we kept the blades sharp and did basic engine maintenance like changing the oil and filter, we could just abuse a push mower all over the golf course for 50 hours a week summer after summer.