Why are American cars like Chevrolet have become so unreliable?

Why do people always recommend a Toyota or Honda over American.

I was thinking of buying a Chevy Malibu or Impala but people don't recommended due to being unreliable cars

The reliability of GM products is improving.
It is not that GM products have become more unreliable, it is that how unreliable they are has become apparent!
Some time go to the library and dig out old "Consumers Reports Buyers Guide".
I have been shopping and buying cars from the 1960's to today. I also know more about corporate ties then some people. Toyota suffered about a decade ago from its ties with GM. The quality of Toyota's dropped to the same level as that of GM. GM and Toyota had a lot of co-venture parts and plants. Toyota came to its senses and ever sense the bankruptcy of GM quality has become a prime concern.
As for Honda, they should have stuck with motorcycles!
By the way a lot of Honda products and Toyota products are actually US made cars. So the problem is not the US auto worker.
There are two places companies pay warranty costs. One is by building it in and the other is by fixing what breaks. GM has always been good about using the replacing what breaks under warranty counting of fixing the problem out of warranty to keep dealerships open. That is a simple fact!

Chevrolets are reliable cars today.

Its probably got something to do with the utter contempt GM has for ordinary people. GM stole $150 billion dollars from the Australian people why I can't say general motors with out spiting on the ground their cars are 2nd rate have been for the last 20 years.

GM cars SUCK. Buy a Honda instead.

The reliability and quality of American brand cars have improved over the years, but Asian brands have improved even more during the same time.

Good point…

Alot of people drive Chevy cars so they can't be that unreliable. It is true though that Toyota and Honda is the best in reliability but only when it comes to there old cars. New Honda cars I heard have not been there best.