Sed is dumping the entire file

I'm trying to parse contents of an HTML file to scrape a download directory, however I've modified it to a MWE that reproduces my issue:

sed -e 's|\(href\)|\1|' index.html

Prints the entirety of index.html. I was originally thinking that it was an issue with my expression, but this very basic expression proves that wrong.

The same happens if I remove -e or if I add g at the end.

It's been a while since I've done sed, am I doing something wrong here? Is sed getting confused with the characters in an html file?