There are people who are actively involved in volunteer activities.
On the other hand though, there are those who have no interest in them.
ご質問ありがとうございます。
"There are people who are actively involved in volunteer activities."＝「ボランティア活動に積極的に関わっている人々がいます。」
"On the other hand though,"＝「もう一方では」
"there are those who have no interest in them."＝「それらに興味がゼロの人々もいます。」
ご参考に。
There are some people who are not interested in doing any kind of volunteer work.
この場合、次のような言い方ができますよ。
ーThere are some people who are not interested in doing any kind of volunteer work.
「どんなボランティア活動にも興味がない人もいる」
volunteer work で「ボランティア活動」
ご参考まで！
アメリカ合衆国 
カナダ 
