The active ingredients are exactly the same. The inactive ingredients may differ and there may be some slight differences in bioavailability that for most people are not significant. There is no reason that the vast majority of people can't take a generic equivalent of a branded medication. That said, there are sometimes exceptions that need to be considered on a cases-by-case basis. Anyone who says "I can't take generic medications" is full of shit.

Source: I am a licensed pharmacist.

With prescriptions, it is not about what the customer wants, it is about what brands the insurance wants to cover (and getting a doctor that does not write a brand specific prescription). If an insurance company only covers a weird brand of a common (but expensive) medicine, the customer either has to hunt for a pharmacy that has it in stock, wait for their local pharmacy to order it (in either case delaying when the insurance company has to pay for it), or buy the in-stock brand without any insurance coverage. The insurance can still claim they cover the drug while paying less for it.

At one point, I was on a medicine that had a very high co-pay for the brand name and would not cover the generic. It was so high that it was cheaper for me to buy the generic uninsured instead of paying the co-pay.

The fun part is the generics aren't always the exact same medication! In most cases it is a 1:1 between name brand and generic but there's always edgecases, whether due to allergies or quality control or sometimes the recipe differences actually impact the potence and performance of the medication

Not all of them are though my wife can only take the name brand of cimbalta because the generic fucks with her body