In what way? The Ramseys responded to written questions. They met with police and prosecutors more than once, and went through several days of questioning.
They became uncooperative when it became clear that the police had little interest in investigating any other theories other than that they were the ones who killed their daughter. The police early on knew they had unidentifiable DNA in JonBenet's underwear, and an unidentifiable palm print at the crime scene. Instead of looking into those leads,
they invented excuses to continue to focus on the Ramseys. At some point, I don't blame the Ramseys for becoming uncooperative. But they sure weren't from the start.