to be fair, it's pretty hard to prove that the second inventor had no knowledge of the invention.
In software where nobody looks at patents, being ignorant of someone else's patent is the common case (and combined with the low-quality 'inventions' getting patent approval, it makes for a really bad case)
but the case law was created in a time and environment where it was common for inventors to be very aware of patents that were being approved in their field.
Also, If you can examine something that includes an invention, it's frequently much easier to duplicate it.