As someone who has worked in the industry, this hasn't been my observation at all. There is never "one" patent for a drug and candidates tend to be patented quite early, so the clock starts ticking. A company may be lucky to get several more patents, but it's not guaranteed.

Plus, there is nothing stopping another company from making a similar drug and beating you to market - there were over 6 -statin drugs in the market at one point.