At least since 1999, that is true. Not only would they not schedule a home and home series with out-of-conference competition, they wouldn't even agree to a "two for one" series out-of-conference - meaning, we'll play two in Cameron for just one game in our place. When Bruce Pearl was here, he tried to get them to agree to a two for one, but Coach K wouldn't do it.
Now, in fairness, prior to '99 they played several home and home series, including a memorable one with the Fab 5 of Michigan in December of 1991 and December of 1992.