[simonh]

Prior art is very difficult to prove and patent reviewers often miss obvious examples. They can't so easily ignore a pre-existing patent. It also protects the invention from exploitation by foreign competitors, in jurisdictions with reciprocal patent protection.

[bloak]

It depends, obviously. Prior art is easy to prove by pointing at an existing patent. It is also easy to prove by pointing at an article in a mainstream publication in the local language. So "protective publication" or "defensive disclosure" is a reasonable alternative to getting a patent (and perhaps letting it expire at the first opportunity).

Prior art is only difficult to prove if you're relying on something along the lines of folk knowledge among the indigenous peoples of the lands where the Jumblies live.

It's non-obviousness that is notoriously difficult to prove.