There does not appear to be a canon answer. However, one may extrapolate from the way the Jedi approach problems. Luke is constant being advised to feel the Force. These feelings can be easily clouded by thoughts (many characters are advised to "empty their mind" when they are having trouble using the force). It would be reasonable to assume Yoda and Obi Wan felt such a significant piece of knowledge would could Luke's ability to feel the Force around him, making him weak. And, as Praxis pointed out, such knowledge is not one that one empties from their mind easily.

Besides, it's all lies anyway! We all know Obi-wan killed his father until the magic of post production changed our reality forever :)

There does not appear to be a canon answer. However, one may extrapolate from the way the Jedi approach problems. Luke is constant being advised to feel the Force. These feelings can be easily clouded by thoughts (many characters are advised to "empty their mind" when they are having trouble using the force). It would be reasonable to assume Yoda and Obi Wan felt such a significant piece of knowledge would cloud Luke's ability to feel the Force around him, making him weak. And, as Praxis pointed out, such knowledge is not one that one empties from their mind easily.

Besides, it's all lies anyway! We all know Obi Wan killed his father until the magic of post production changed our reality forever :)

There does not appear to be a cannon answer. However, one may extrapolate from the way the Jedi approach problems. Luke is constant being advised to feel the Force. These feelings can be easily clouded by thoughts (many characters are advised to "empty their mind" when they are having trouble using the force). It would be reasonable to assume Yoda and Obi Wan felt such a significant piece of knowledge would could Luke's ability to feel the Force around him, making him weak. And, as Praxis pointed out, such knowledge is not one that one empties from their mind easily.

Besides, it's all lies anyway! We all know Obi-wan killed his father until the magic of post production changed our reality forever :)

There does not appear to be a canon answer. However, one may extrapolate from the way the Jedi approach problems. Luke is constant being advised to feel the Force. These feelings can be easily clouded by thoughts (many characters are advised to "empty their mind" when they are having trouble using the force). It would be reasonable to assume Yoda and Obi Wan felt such a significant piece of knowledge would could Luke's ability to feel the Force around him, making him weak. And, as Praxis pointed out, such knowledge is not one that one empties from their mind easily.

Besides, it's all lies anyway! We all know Obi-wan killed his father until the magic of post production changed our reality forever :)