Passé simple

Question

Why is there so much emphasis on this when it’s only used in serious written French.

Accepted Answer

No expert, but 
1. The passé simple is in the C1 syllabus 
2. If you want to read books in French, it comes up frequently and isn’t always intuitive to understand, eg je fis/je fut, je vit/je vécut 
3. It isn’t only written French - for example President Macron very often uses it in his speeches to refer to distant events, presumably to add a sense of history. 
 Also, I get the impression that there are far fewer topics for C1 on this site than for other levels (A2 for example), so individual topics do seem to come round more often.

Answer

Bonjour Liz,
To supplement Anne's answer, Le Passé Simple is also used in journalistic work. So it will feature regularly in newspaper articles. Take a look here: When should you use the passé simple instead of other past tenses
I hope this is helpful.
Bonne journée !