You're just saying that because you don't have much interest in baseball.
You think that because you're not a baseball fan.
この場合、次のような言い方ができますよ。
ーYou're just saying that because you don't have much interest in baseball.
「あなたは野球にあまり興味がないからそう言うんでしょ」
don't have much interest in ... で「…にあまり興味がない」
ーYou think that because you're not a baseball fan.
「あなたは野球ファンじゃないからそう思うんだよ」
ご参考まで！
カナダ 
