10 years is drastically simplifying things.

There are patents on various parts of the drug including the molecule, delivery mechanism(s), process to manufacture it, etc. Each patent is separate and has its own lifespan. Generally speaking, they last 20 years from when they're filed for modern patents.

Since any form whatsoever of public disclosure could jeopardize the ability of the drug manufacturer to get and enforce their patent, they generally file for a patent on the molecule very early - before any real trials start. That means that, by the time the drug is actually approved and on the market for general use, there may be more like 5-7 years left. 10 would be pretty amazingly fast in terms of approval, actually.

The other types of patents are easier to get around early disclosure on, and they generally come from later developments, anyway.

It's pretty common for the patent on the basic molecule and even delivery means to be expired but for a patent on the most economic means of manufacturing to still be in force. Sometimes this is the result of process engineering and refinement years later. This can remove the economic incentive for generics since they're then stuck using old manufacturing techniques even if they could legally bring the product to market without infringing the basic patents.

What is really shady are some of the patents on a particular use of a drug. It's sometimes possible to get a drug approved for a new indication, get a patent on that, and then claim that "well since we have a patent that's still in effect on this particular use and the actual end use of the product is uncontrolled, no generics can exist in the market". This has become a popular way to extend patent protection lifetimes on some classes of drugs and probably needs to be clamped down on.

Note that getting a drug developed and through trials and FDA approval costs billions of dollars in the USA for a success, and you also have to cover the inevitable failures and still turn a profit. If you're going to rely on commercial development (and the fact that a lot of the basic research is government subsidized probably needs to be more heavily considered, here...), you have to provide SOME means of making back the money.

Now marketing costs...that's another matter.