I work in the industry, it mostly depends on the class of the drug. Drugs derived from traditional "small molecule" chemistry tend to be a lot faster than "large molecule" biologics. A "large" small molecule like Lipitor might be made from around a hundred individual atoms and have a mass of about 1,000 Daltons. A Biologics derived drug like Humira might be around 150,000 Daltons, or more depending on what it is.

From a manufacturing perspective the complexity of a small molecule is on the relative scale of creating identical bicycles vs building an identical aircraft carrier. The first is a challenge, but you can usually prove atom by atom that the new product is in fact identical meaning it can go for sale quickly. The latter is actually impossible, no two ships are identical in final construction and that's assuming they're from the same shipyard. A rival country trying to recreate an aircraft carrier from scratch? No chance it's the same. So what the rivals actually do is try to produce a "biosimilar" and bring that to market. That involves a hell of a lot more work and a lot of long expensive clinical studies proving that thir biosimilar is no-par with the original product.

A secondary factor is market size. There's a fixed cost to setting up a production line, if the drug is for a rare disease then you're splitting the cost fewer ways.