It's a failure of feedback that makes this happen.
If people can't get reliable information about quality, quality will not determine what they buy. Price will, and price is readily available. To get price down, you need costs down. To do that, you replace the parts with crappy parts.
If feedback worked, people would know they were paying less for a less good appliance that will have more downtime, and they would act accordingly.
Part of it is statistical noise: you only get to use so many washing machines in your life, and you may or may not have big problems with them. Your only direct evidence on quality then depends on this roll of the dice.
Part of it is lack of competition: only 4 competitors. You only need to be in the ballpark of "OK" to sell. You're not scratching around for every customer, there's definitely going to be some. So why spend a lot of money making your machine more reliable?
Part of it is cost of information: how much time are you going to spend finding this information? You'll need to learn a bunch of technical terms. And how do you find trustworthy reviews? Most likely reviews are another source of noise, for the same reason as mentioned. So information is expensive to get and anyway if you're right about the manufacturers being the same it's also worthless!