Tires are a simple, well-known product, whereas medicine is not. Drug discovery happens to be a billion dollar process that often results in failure. All of the low-hanging fruit have been taken, and the remaining solutions all require intense research. Though a compound or antibody or whatever might be cheap to replicate once elucidated, you still have to pay the price for the process.

Marketing then directs dollars to product. Drugs often target a very specific healthcare niche, which requires massive education campaigns. Everybody knows that they need tires. Not everybody knows about the existence of a novel drug that solves a medical problem that only a subset of the population encounters.