There are some brands of bicycles that can cost more than the down payment on a car. Why? Surely making a bike lightweight and reliable isn’t so difficult that it warrants that price? Is it just the brand name or maybe it has to do with customization options?
To be fair, the OP did say “some brands” not ALL bikes. Also, I have one of those Walmart bikes and I pity the foo who owns one. On my very first ride, my pants tore the chain guard off. Pretty sure it was there to protect my pants. Then when I came to a stop, the seat exploded. Springs, nuts, bolts and washers went flying. I had to gather them up again and try to piece it back together to keep the seat usable. It’s ridiculously heavy too. If you can’t afford a nice new bike, I recommend buying a decent used one at a garage sale or something. I don’t agree that they will serve the vast majority of people just fine.
Not to “victim blame” because such unsafe junk should not be sold. But a $100 bike with amortized seat and spring suspension of wheels has no right to be durable. But an $100 simple bike with shimano gears or no gears can last for years.
In a nut shell, I had an older but better built bike at work I used to get around campus. Someone borrowed it and did not bring it back. Eventually it was found in a work area where it was destroyed by a steal beam they dropped on it. The construction supervisor gave me $100 to buy a new one, so I went to Walmart. It appeared that they were all built the same. I noticed the warning sticker on the bikes were identical between makes leading me to believe they were just the same cheap bikes with different brands. So I bought the one that did not have coaster brakes. I hate coaster brakes. I still have it and use it as a spare bike. It’s trash, despite being the most expensive bike I’ve ever bought. My current bike was given to me by a friend who was not using it. She said it was a $400 bike. Anyway, I digress, but that’s why I bought such a cheap bike. The circumstances were just right. Don’t want an expensive one just sitting outside at work. Plus I could use a company truck to go get it during lunch, instead of shopping around for a better used one.