YOU SAID:

There are those who have not been able to do so, because they have not been able to do so.

INTO JAPANESE

できなかった人たちもいます。

BACK INTO ENGLISH

Some people could not.

INTO JAPANESE

できない人もいました。

BACK INTO ENGLISH

There were people who could not.

INTO JAPANESE

できない人がいました。

BACK INTO ENGLISH

There was a person who could not.

INTO JAPANESE

できない人がいました。

BACK INTO ENGLISH

There was a person who could not.