Because otherwise your answer will not be accepted in this course. It is as simple as that.
There are too many spellings of the English translation of Kateřina: Catherine, Katherine, Katharine, Katrina, etc. Also, in general it is not good practice to translate someone's name. If Jane Doe travels to Spain, her name does not become Juana.
When I listen to this at normal speed, the speaker sounds as though she says ona for Matěj. But when I listen at half speed, it is clearly on. But then I put it at normal speed again, and I distinctly hear ona.
I did use to the REPORT button for this; just curious to know if anyone else hears what I hear.