It's very difficult to develop new drugs, and the reason it's difficult to develop new drugs is because in the early stages of drug development, the drugs are very risky, and they're very expensive.
Разрабатывать новые лекарства  очень сложно. Причина такого положения в том, что на ранних стадиях разработки лекарства опасны и очень дороги.