Back when Google was young they offered a keyword tool to anybody. When they went public (offered stock in the company) they needed to report profits. Bandwidth is an expense. The public keyword tool was a casualty because it was a resource hog. They replaced the public tool with their keyword planner tool under their adwords product area. You needed an adwords account to use the tool but you did not actually need to buy advertising with adwords. Evidently enough people learned of this so that the tool became a noticeable resource hog without expected return on investment so they discontinued it under adwords again. The last couple of posts offer a current work around so that you can still get some keyword data directly from Google.
Very informative and very experienced post which was mentioned about inception days and after going public. Google these days Become so much commercial with ads and charges.