Grell was initially going to do STARSLAYER for DC, but Pacific Comics gave him a better offer of creator ownership and profit-sharing. It's possible that rubbed DC the wrong way.
Grell didn't do work for DC (except for a few pin-up pages in Batman and Superman 400th anniversary issues) until he came back to do THE LONG BOW HUNTERS in 1987.
I recall Grell coming back and scripting a lot of Green Arrow crud in the late 1980's though.
