What you are describing is called "Product Lifecycle Managment"
http://en.wikipedia.org/wiki/Product_lifecycle_managementBasically, if your business is to make and sell microwave ovens, you want to ensure that you do not saturate the market with durable goods that last too long, but also that your products are not so inferior in workmanship that they break on first use. A great deal of research and development into materials and manufacturing practices/standards is employed to meet these requirements in the durable goods marketplace.
Tools, for instance, often focus on being of high manufacturing quality if they are a name brand-- OR, they focus on being just barely fit for function, if they are a cheap disposable one. (The difference between a name brand tool brand, like Snap-on or craftsman, VS commodity crap like great-neck or harbor freight.)
It isnt so much a conspiracy-- so much as it is an open business practice. Before the rise in globalist consumerism, producing the best possible quality of durable good was the ideal that all manufacturers strove for, and durable goods were over-built. Look at this electric drill gun from the 1940s, for instance.
Compare it with a contemporary electric drill
The former has all-metal exterior housing, the cord attachment to the handle has a longer and studier rubber support grommet, and is placed at a lower contact angle to avoid it being bend or kinked, it has a ruggedized keyed chuck for the tool holder, and was designed for aggressive, heavy, and sustained use. With proper care, such a tool could last for over a hundred years, and remain serviceable.
The latter has much of its exterior housing composed of polymers, has a plastic clutching chuck which can fail under normal workloads, the cord angle is such that the connection near the main body could become kinked and produce shorts in the wire over time, and is clearly intended to be replaced after about 5 to 10 years.
You are not wrong to wonder why things dont last longer.
The reason is simple: The people that make things would not stay in business if they made products that can last for 100 years or more-- People would pass down perfectly servicable durable heirlooms instead of buying new ones.
In the consumer world, this practice has the rather sordid appellation of
"Planned obsolescence". You can find some very poignant examples of this in the Apple "iDevice" lineup. Just ask somebody that needs a lightning cable how they feel about the cable being redesigned with every new iteration of iphone, for instance.
In this day and age, if you want a quality product that is built to last, you have 2 choices.
1) Look for an antique that was built that way (Like that drill. Estate sales are a GREAT place to look!)
2) Make the product yourself, and pay slavish attention to workmanship and durability.
I am currently in the process of doing the second one on a hiking backpack I am building. I am fabricating it from 300lb test cordage to produce the main backpack fabric. I will be able to load it with platinum nuggets and hoist it from a crane, and not rip it, if I were to feel so inclined. When I am done with it, I fully expect it to last longer than I do.