Academics aren't always concerned with making your job easy, they have lives too. They may have struggled a lot for their results and their code is still a living document, or they sell it to a company. Maybe their grant ran out and they got pulled into something else. Maybe they died.

There's a lot of factors.

Look at OpenRave. It's the result of an academic open sourcing his research.

I just think at the end of the day, a research paper exists to validate human understanding of nature - not give you a boilerplate for implementing it.