I wonder if that has to do with the fact that he kinda let the cat out of the bag about Vader being Luke's father?
That’s false claims... and a rumor, prowse mentioned in a interview/article back in 78 to British press, “wouldn’t it be a kind of twist if Luke and Vader were related”
That snow balled into all kinds of rumors that prowse let out this huge secret when in fact George never mentioned the relationship and I personally didn’t believe he even thought of the relationship between the 2 at the time
To back this up, prowse got very anger when he saw the empire strikes back debut with the cast and Lucas there in the theater..
Prowse’s line was “Obi-Wan killed your father..” and prowse has said on record at the time he believed Vader was lying to Luke
Lucas only told Hamill that the real line was what it is today, and he only told Hamill that because he wanted to have Hamill pull off a very heart breaking scene...
Prowse was enraged that Lucas didn’t trust him with this information
I don’t believe anyone other then Lucas, fishner, Kurtz and Hamill knew of it back then..
I’m not saying or defending prowse.. he is no angel..
But there was more bad politics involved that kept prowse locked in his trailer.. but that’s a thread for a whole other day..