...because CLAMP stopped writing new stuff and started recycling old stuff. The main characters of TTR are Sakura Kinomoto and Li Shaoran from Cardcaptor Sakura. But it's not a sequel to CcS; no. It's a story in which Sakura has lost her memory and she and Shaoran have to jump from reality to reality collecting the fragments of Sakura's memory, and Mokona (the mascot from Magic Knight Rayearth) and Emeraude (also from MKR) are in it, and Sumomo from Chobits, and God alone knows who the hell else.
Yeah: "Well, what can we do to top our previous big hits? I know! Let's just combine them all into one big morasse!"
...this may be the OVA series, not the TV series. I don't care either way. TTR is one I'm staying very, very far away from.